GPT-6.1 Sol vs Claude Opus 5.5: Half the Price, 1/6 the Task Cost

As of October 10, 2026, GPT-6.1 Sol lists at $2 per 1M input tokens and $10 per 1M output tokens, half of Claude Opus 5.5's $4 and $20. Measured per task, the gap is wider. At medium effort, the default on both models, Artificial Analysis records $0.21 per task for Sol and $1.34 for Opus 5.5, so Sol costs about one sixth as much. Opus 5.5 scores higher at every effort level except low, where the two tie at 42, and its lead grows to 6 index points at max effort.

Both vendors now sell a faster tier of the same model. GPT-6.1 Sol Ultrafast went live on October 8 at $12 / $60 per 1M tokens and is open to every API account. Opus 5.5 Fast mode costs $8 / $40 and is a waitlisted research preview on the Claude API.

A workable starting position:

• Default to GPT-6.1 Sol for high-volume coding, agent and document work that tests or scripts can check, as long as requests stay at or under 272,000 input tokens.
• Keep Opus 5.5 where each failed attempt costs a person real review time, for hard problems you would run at high or max effort, and for prompts that regularly pass 272K input tokens, where Sol's price edge shrinks to a few percent.
• For speed, compare per task, not per token. One identical request costs 1.5× more on Sol Ultrafast than on Opus Fast mode, but Opus writes about three times as many tokens per task. Estimated per Artificial Analysis task, Sol Ultrafast costs about the same as standard-speed Opus 5.5 and about half as much as Opus Fast mode.
• Settle it with your own pass rates. The cost-per-accepted-result rule turns two pass rates and a review cost into an answer.

Every figure below carries its source and settings, and vendor-run benchmarks are labeled as such.

Which to use: GPT-6.1 Sol or Opus 5.5, by workload

What GPT-6.1 Sol is, and where each model is available

"GPT 6.1" (often written "Sol 6.1") is one model: GPT-6.1 Sol, API ID gpt-6.1-sol. OpenAI introduced it at DevDay as an upgrade to GPT-6 Sol, and the API changelog dates the release to September 29, 2026. There is no GPT-6.1 Astra and no GPT-6.1 Luna. OpenAI says GPT-6 Astra remains its most capable model.

Claude Opus 5.5 (claude-opus-5-5) was released on September 22, 2026. Opus 5 (claude-opus-5) is the previous Opus, so benchmark rows labeled "Opus 5" describe an older model.

Sources: OpenAI's GPT-6.1 Sol model page and Anthropic's Opus 5.5 overview, as of October 10, 2026.

One detail trips up people who mostly chat. On October 7, OpenAI brought GPT-6 to the ChatGPT Chat tab as GPT-6 Sol for paid plans and GPT-6 Luna for Free and Go. That is not GPT-6.1 Sol. OpenAI's ChatGPT pricing page still says GPT-6.1 Sol is available "in Work and Codex, not Chat."

API price at standard speed: half per token up to 272K input

All prices are USD per 1M tokens on each vendor's direct API, before tax.

Sources: OpenAI API pricing and Claude API pricing. Bedrock and Google Cloud set their own Opus 5.5 prices.

GPT-6.1 Sol's rate is not a launch promotion. OpenAI's pricing page does carry a note that promotional pricing is "available at least through November 21, 2026," but that note names GPT-5.6 Sol only. Neither vendor says how long its current GPT-6.1 Sol or Opus 5.5 prices will hold.

Long prompts: what changes past 272K and near 900K

OpenAI bills any request with more than 272,000 input tokens at 2× the input and cache rates and 1.5× the output rate, for the whole request. Anthropic bills Opus 5.5's full 1M context at the standard rate. The examples are uncached.

Exactly 272,000 input tokens stays at the short rate. One thousand more tokens raises the Sol request from $0.744 to $1.392, an 87% jump, while the Opus request rises by $0.004. Above the line both models charge $4 for input, and only Sol's $15 output rate keeps it ahead.

A 900,000-token prompt fits on both, but Sol's ceiling is 922,000 input tokens, while Opus 5.5 accepts up to its 1M context. If your prompts hover near 272K on Sol, trimming them under the line saves more than any other change. If they sit well above it, token price stops being a reason to switch.

Speed tiers since October 8: Sol Ultrafast $12/$60 vs Opus Fast mode $8/$40

Both vendors now sell the same model at a higher speed for a higher price. Neither tier is a separate model.

Above 272K input, Sol Ultrafast costs $24 input, $1.20 cache read, $30 cache write and $90 output. Opus Fast mode stays at $8 / $40 across the full context window. Sources: OpenAI's pricing page and Ultrafast guide; Anthropic's fast mode docs.

Who can use each speed tier

Two consequences matter in practice. Buying credits on Plus, Pro 100 or Pro 200 does not unlock Ultrafast in Codex; OpenAI's Codex speed docs say other self-serve plans have no access at launch "even with purchased credits." And on the Claude side, switching between fast and standard speed invalidates the prompt cache, because the two speeds do not share cached prefixes.

One request at every speed tier

Same token counts on every tier, list prices, at or under 272K input, cache writes left out:

The ratios hold in both mixes. Sol Fast costs the same as standard Opus 5.5. Sol Ultrafast costs 1.5× Opus Fast mode, 3× standard Opus and 6× standard Sol. The Opus Fast cache-read price of $0.40 assumes the usual 0.05× cache multiplier applied to the $8 fast input rate, which is how Anthropic says the multipliers stack.

Long prompts widen the gap. A 900,000-token request with 10,000 output tokens costs 0.9 × $24 + 0.01 × $90 = $22.50 on Sol Ultrafast and 0.9 × $8 + 0.01 × $40 = $7.60 on Opus Fast mode.

Per task: Sol Ultrafast costs about as much as standard Opus

Equal token counts flatter Opus 5.5, because it writes far more tokens per task. Both fast tiers run the same model, so a reasonable estimate multiplies Artificial Analysis's measured cost per task by each tier's price multiple: 6× for Sol Ultrafast, 2× for Opus Fast mode.

At medium effort, Sol Ultrafast lands close to standard Opus 5.5 and at about half of Opus Fast mode. These are estimates. Nobody has published a measured run of either fast tier, and they assume the faster tiers use the same tokens as the standard ones.

What the speed claims do and don't tell you

OpenAI says Ultrafast is "up to 8x faster" than Sol Standard. Anthropic says Fast mode gives "up to 2.5x higher output tokens per second" than standard Opus. Each figure is a vendor maximum against that model's own standard speed, so they can't be compared with each other or turned into seconds saved. Both describe output-token speed. Anthropic states that Fast mode does not target time to first token, and OpenAI recommends a WebSocket connection to keep Ultrafast's gain. No independent tokens-per-second measurement of either tier has been published, so posts claiming Sol Ultrafast "barely keeps up" with standard Claude are opinion, not data.

What is measured is standard speed, and it splits two ways. On Artificial Analysis at medium effort, Opus 5.5 streams at 79 output tokens per second against Sol's 52, but Sol returns its first answer token after 5.9 seconds against Opus's 21.9. Sol still finishes the average task sooner, 156 seconds against 199, since it writes about a third as many tokens. Vals reports 43 minutes per test for Sol and 1 hour 19 minutes for Opus 5.5.

Benchmarks by effort: tied at low, Opus ahead by 6 points at max

Artificial Analysis at five effort levels

Artificial Analysis's release comparison now covers both models at all five effort levels. Its Opus 5.5 rows are labeled "Default Fallback"; the fallback section explains what that changes.

Values as of October 10, 2026. The page is updated as runs change, and speeds depend on load and route.

Three readings are worth acting on:

• The gap opens with effort. At low effort the two models score the same, and Sol costs about a quarter as much. At medium Opus leads by 3, and the lead grows by one point at each level above that.
• Sol at xhigh matches Opus at medium. Both score 51. Sol does it for $0.39 per task against $1.34, about 3.4× cheaper. The price is time: 173.7 seconds before Sol's first answer token, against 21.9 seconds for Opus. Sol at max scores 52 for $0.72, one point above Opus at medium for 54% of its cost per task.
• Neither model is uniformly faster to respond. Sol starts answering sooner at low, medium and max effort; Opus does at high and xhigh. Opus streams faster at every level.

On Terminal-Bench 4.0 inside the same suite, the coding-agent test, Sol scores 48.0% at medium and 56.1% at max, against 52.5% and 59.6% for Opus 5.5.

Vals Index: 5.8 points apart, 3.9 if fallback counts as failure

The Vals Index v2.1, updated October 7, 2026, weights finance, coding, legal and tax tasks:

Opus 5.5 scores 5.8 points higher at about 9.9× the cost per test. Vals notes that part of Opus 5.5's score comes from tasks a fallback model answered after a refusal. Counting those tasks as failures lowers Opus 5.5 to 65.05%, and the gap to Sol shrinks to 3.9 points. Effort settings per row aren't listed.

OpenAI's launch charts: the winner flips with effort

OpenAI's announcement compares the two on its own choice of benchmarks. OpenAI ran its models itself, took competitor results from public reports and labels Opus 5.5 "with fallbacks."

Even in the vendor's own charts, Sol wins at medium and high effort, and Opus 5.5 wins at max. Anthropic's Opus 5.5 launch tables (Terminal-Bench 4.0 at 66.4%, OSWorld 2.1 at 81.8%) have no GPT-6.1 Sol row, and Sol's published OSWorld 2.0 score is a different version, so Anthropic's numbers can't be set against Sol's.

The "Default Fallback" label on Opus 5.5 rows

Opus 5.5's safety classifiers can decline a request. The API returns a normal HTTP 200 with stop_reason: "refusal". If you turn on server-side fallback (fallbacks: "default" with the beta header server-side-fallback-2026-07-01), the API retries on the model Anthropic recommends for that refusal category. Anthropic routes most cybersecurity tasks to Opus 4.8.

For a comparison, that means three things:

• Published Opus 5.5 scores are partly another model's. "Default Fallback" on Artificial Analysis, the Vals footnote and OpenAI's "with fallbacks" all describe Opus 5.5 plus its fallback.
• Fallback is opt-in. Without it, the refusal stands and your code has to handle it.
• Each attempt is billed at the rate of the model that ran it. Refusals that produce no output are billed only in the bio, frontier_llm and reasoning_extraction categories, since September 24, 2026.

If your prompts touch security tooling, measure the refusal rate on your own tasks before trusting any published Opus 5.5 score.

Token counts: why Opus 5.5 costs 4–9× more per task

A 2:1 price per token becomes 4–9:1 per task because Opus 5.5 writes much more. On Artificial Analysis's medium pair, Opus 5.5 used 26k output tokens per task against Sol's 8k, 12k of them reasoning against 3k. At max effort it was 119k against 38k, with 84k reasoning tokens against 25k. Three times the output at twice the output price already makes about six times the output bill. On Vals the totals were 477.68M output tokens for Opus 5.5 and 104.77M for Sol.

Two caveats apply when you translate this to your own text. Anthropic says the tokenizer used since Claude Opus 4.7 produces about 30% more tokens for the same text than its previous one, and no published figure compares Claude's tokenizer with OpenAI's. Artificial Analysis also reports two different cost metrics: cost per task (6.4× at medium, 8.3× at max) and cost to run the whole index ($361 vs $1,627 at medium, 4.5×; $1,082 vs $8,708 at max, 8.0×). Quote one or the other, not a blend.

To estimate your own ratio, run the same 20 to 50 representative tasks on both models, sum the usage fields from the responses and multiply each side by its rates. For requests at or under 272K input:

Bill ratio ≈ 2 × (Opus 5.5 billed tokens per task ÷ Sol billed tokens per task)

If Opus uses 1.5× the tokens on your tasks, expect roughly a 3× bill; at 3×, roughly 6×. Effort is the main lever on the Opus side, and choosing and measuring an Opus 5.5 effort level covers how to set it.

Cost per accepted result: decide with your own pass rate

Token cost is only part of what a result costs. Someone or something checks each attempt, and failed attempts get retried. If one attempt costs c in tokens and R in review, and passes with probability p:

Expected cost per accepted result = (c + R) ÷ p

Opus 5.5 is the cheaper choice only when:

p(Opus) ÷ p(Sol) > (c(Opus) + R) ÷ (c(Sol) + R)

R and both pass rates are your inputs. The examples use Artificial Analysis's medium-effort cost per task ($0.21 and $1.34) as c; replace them with your measured cost per task when you have it.

Automated checks, R = $0. The right side is 1.34 ÷ 0.21 ≈ 6.38. Even an Opus 5.5 that never fails wins only if Sol passes fewer than 1 ÷ 6.38 ≈ 15.7% of attempts. Checking both sides: Sol at 15% costs $0.21 ÷ 0.15 = $1.40 per accepted result, more than a perfect Opus at $1.34; Sol at 20% costs $1.05, less. When tests do the reviewing, Sol wins unless it almost never works.

Human review, R = $5 per attempt (five minutes at $60 an hour, for example). The right side is (1.34 + 5) ÷ (0.21 + 5) = 6.34 ÷ 5.21 ≈ 1.217. If Sol passes 70% of attempts, Opus 5.5 has to pass more than 0.70 × 1.217 ≈ 85.2%.

The more each review costs, the less token price matters, and the smaller the quality edge Opus 5.5 needs to pay for itself. The same holds on the fast tiers. With the per-task estimates above (≈ $1.26 for Sol Ultrafast, ≈ $2.68 for Opus Fast mode) and $5 review, the threshold is 7.68 ÷ 6.26 ≈ 1.227, so Opus Fast needs to pass more than about 85.9% against Sol Ultrafast's 70%.

The rule assumes you retry until something passes and that reviewing either model's attempt takes the same time. If Opus 5.5's longer output takes longer to read, raise its R.

ChatGPT and Claude plans: Ultrafast on Pro $500, no Opus allowance number

The two $20 plans can't be compared by a published figure, and dividing the monthly fee by API prices doesn't produce one. What the vendors do state:

Sources: OpenAI's ChatGPT pricing and Pro tiers help article, Anthropic's plans page. The Max credits are covered in Claude Max API credits: how to claim and use $100–$200 a month.

Three widely shared claims need context:

• "OpenAI halved the $200 plan." OpenAI's help article says new Pro 200 subscriptions "include a lower usage allowance" at the same $200 price, and that anyone subscribed between September 22 and 10 a.m. Pacific on September 29, 2026 keeps the previous allowance through October 29, 2026. OpenAI gives no size for the cut. "Halved" is SemiAnalysis's figure from its own tracking.
• "Claude plans give 5× the value." SemiAnalysis (October 6, 2026) estimates that Claude plans give about 5× the API-equivalent value of GPT-6.1 Sol plans for agentic work (about 4× in another passage). It measured the usage meters and priced the tokens at list API rates for its own September workload. Because Opus tokens list at twice Sol's price and Opus writes about three times as many tokens per task, 5× the value does not mean 5× as many finished tasks.
• "Sol got 50% faster." OpenAI's Tibo Sottiaux posted on October 5 that default speed for GPT-6 Astra and GPT-6.1 Sol was optimized to be "~50% faster" through the subscription, including partner tools using Sign in with ChatGPT. The post says nothing about the API and gives no tokens-per-second figure.

If you mostly chat, GPT-6.1 Sol isn't in ChatGPT Chat at all. If you already pay for one plan, count how many of your usual tasks finish inside a five-hour window for a week before paying for the other. If you hit limits daily, the API prices above are the comparison that applies to you.

Switching existing code to GPT-6.1 Sol or Opus 5.5

From GPT-6 Sol to GPT-6.1 Sol: input and output stay at $2 and $10, the 272K rule is the same, and cache reads drop from $0.20 to $0.10 per 1M. Three changes can break calls. gpt-6.1-sol rejects reasoning effort none and minimal, so low is now the floor, and those calls will reason where they didn't before. Tool calling works only through the Responses API; Chat Completions works without tools. Ultrafast is Responses-only too. OpenAI's usage tiers were also renamed on October 6 from five numbered tiers to Build, Launch and Grow. Prices across the rest of the family are in GPT-6 Luna vs. Sol pricing, and Sol's faster tiers are compared with Astra's in OpenAI Ultrafast vs Sol.

From another model to Opus 5.5: changing the model string isn't enough. Anthropic lists four breaking changes for code written for Opus 5: thinking can't be disabled, forced tool use returns an error, thinking blocks are tied to the model and conversation that produced them, and the older computer_20251124 tool is rejected on the Claude API and Google Cloud. Text between tool calls now arrives in thinking blocks that are empty at the default display setting. Handle stop_reason: "refusal" or enable fallback. The full list of checks is in Claude Opus 5.5: API price, model ID, and migration checks.

Any other models to consider: Sonnet 5.5, GPT-6 Astra, Gemini 4 Argon

• Claude Sonnet 5.5 lists at the same $2 / $10 as GPT-6.1 Sol, with cache reads cut to $0.10 on October 7. On Vals it scores 67.04% at $21.34 per test, level with Opus 5.5. If you want Claude behavior at Sol's token price, test it first.
• GPT-6 Astra is OpenAI's top model at $10 / $50 and scores 63.13% on Vals. GPT-6 Astra access covers where it runs on ChatGPT plans.
• Gemini 4 Argon leads the Vals Index at 68.90%, but it isn't generally available in the paid API. The Gemini 4 Argon vs Claude Opus 5.5 vs Sonnet 5.5 comparison covers access.
• GPT-5.6 Sol lists at the same $4 / $20 as Opus 5.5 on a promotional price; Claude Opus 5.5 vs GPT-5.6 Sol compares that pair.

GPT-6.1 Sol vs Opus 5.5 FAQ

Is GPT-6.1 Sol better than Opus 5.5?

Not on the independent indexes, where Sol at best ties. Opus 5.5 matches Sol at low effort on Artificial Analysis and leads by 3 to 6 points from medium to max; it leads by 5.8 points on Vals, or 3.9 if fallback-served tasks count as failures. In OpenAI's own charts Sol scores higher at medium and high effort and Opus 5.5 at max. Sol is far cheaper per task in every one of those comparisons, and at xhigh it matches Opus at medium for about 1/3.4 the cost.

How much cheaper is GPT-6.1 Sol?

Half per token for requests at or under 272K input tokens, and only 1–7% at equal token counts above that. Per completed task, Artificial Analysis measures Opus 5.5 at 4.2× (low) to 8.9× (xhigh) Sol's cost, 6.4× at the default medium effort, and Vals at 9.9× per test, because Opus writes about three times as many tokens. On the fast tiers the per-request order reverses: Sol Ultrafast costs 1.5× Opus Fast mode for the same tokens, though per task it comes to roughly half, by an estimate that assumes each tier uses the same tokens as standard speed.

Is there a GPT-6.1 Astra or Luna?

No. GPT-6.1 exists only as Sol. GPT-6 Astra and GPT-6 Luna remain on their GPT-6 versions, and the GPT-6 that reached ChatGPT Chat on October 7 runs on GPT-6 Sol and GPT-6 Luna, not GPT-6.1 Sol.

How much does GPT-6.1 Sol Ultrafast cost?

$12 input, $0.60 cached input, $15 cache write and $60 output per 1M tokens at or under 272K input; $24 / $1.20 / $30 / $90 above that. That is 6× Sol Standard. It has been live since October 8, 2026 for every API account through the Responses API. In Codex and ChatGPT Work it needs Pro $500 or an eligible Enterprise or Edu plan.

Is GPT-6.1 Sol's price a limited-time promotion?

No. The promotional note on OpenAI's pricing page, "available at least through November 21, 2026," names GPT-5.6 Sol. GPT-6.1 Sol's $2 / $10 carries no promotional label, though OpenAI doesn't say how long any price will hold.

What is still unknown about GPT-6.1 Sol and Opus 5.5?

No one has published measured speeds for Sol Ultrafast or Opus Fast mode, or a neutral head-to-head on an identical harness beyond Artificial Analysis and Vals. OpenAI hasn't sized the new Pro 200 allowance or said whether the ~50% subscription speedup touches the API. Anthropic publishes no numeric Opus 5.5 allowance for its plans, and no one has published a ratio between Claude's and OpenAI's tokenizers.