GPT-6 Sol vs Claude Opus 5.5 vs Grok 4.7: The September 2026 Price War

Last updated: September 26, 2026

Three frontier-class models launched inside 48 hours, and all three repriced the tier they entered. SpaceXAI's Grok 4.7 opened on September 21 at $2/$6 per million tokens. Anthropic's Claude Opus 5.5 arrived on September 22 at $4/$20 with cache reads cut to $0.20. OpenAI answered the same day with GPT-6 Sol at $2/$10 and GPT-6 Luna at $0.10/$0.50. Within hours the comparison charts were pointing at each other's benchmark tables and disagreeing by double digits. This post compares the three launches head to head with same-day-verified prices from the vendors' own pages, separates vendor-reported benchmarks from third-party work, and works through who should move to what.

Official Sources#

All prices below were verified September 26, 2026 against the vendors' live pages:

The Three Launches in 48 Hours#

Grok 4.7 (September 21). SpaceXAI positions it as its most capable coding and knowledge-work model, trained with a longer RL run weighted toward tasks that take hours, with a new safeguard stack (3.3% of risky dual-use prompts pass HackerBench v0.3, per the announcement). It serves at the same price and speed as Grok 4.6: $2 input / $6 output per MTok, with a fast variant at double the output speed for double the price. Available in Cursor, Grok Build, and the Grok API.

Claude Opus 5.5 (September 22). Anthropic's first model in the new Claude 5.5 family (Sonnet 5.5 and Haiku 5.5 are promised "in the coming weeks") performs at Fable 5.1 level on most work at 40 percent lower cost than Opus 5: $4 input / $20 output, cache reads at $0.20 (a 0.05x multiplier, down from the standard 0.1x), and fast mode at $8/$40. It set new highs on Terminal-Bench 4.0 (66.4%) and GDPval-AA v2.1 (1846 Elo). Our full release guide has the benchmarks, the effort-level caveat (at max effort it can over-think into the 128K output ceiling), and the OpenCode setup.

GPT-6 (September 22). OpenAI's new family ships three tiers: Astra ($10/$50, max capability), Sol ($2/$10, the coding-and-agentic flagship), and Luna ($0.10/$0.50, high-volume workhorse), all with a 1,050,000-token context window. Sol at $2/$10 is the first frontier-class model priced below the mid tier, and Luna is the cheapest model OpenAI has ever shipped - cheaper than DeepSeek on every axis. GPT-5.6 stays live: Sol's $4/$20 promo runs at least through November 21, 2026. On September 29 OpenAI shipped GPT-6.1 Sol at the same $2/$10 sticker with cache reads halved to $0.10 and near-Astra agentic scores, while holding back GPT-6.1 Astra over safety concerns.

The Head-to-Head Table#

Standard rates per million tokens, verified September 26, 2026:

Benchmarks, with honest attribution (none of these are independent third-party runs; each vendor published its own table):

The cross-vendor numbers clash on purpose: SpaceXAI's chart scores GPT-6 Sol at 41.7% CursorBench and Fable 5.1 at 51.8%, Anthropic's chart scores Opus 5.5 roughly 11 points above Sol's best, and Terminal-Bench 4.0 splits the field three ways with Opus 5.5 clearly on top (66.4%) and Grok 4.7 far below (37.6%). The only third-party workflow data we have seen this month puts GPT-6 Sol at 79.1% at $0.2152 per run on TypeSafe's workflow evals (fixed code-defined workflows, benchmarked against the average of GPT-6 Astra and Fable 5.1). Treat all of it as directional: run your own golden set before you switch, and note that DeepSeek's V4.1-Flash at $0.15/$0.60 off-peak is still the open-weights reference floor the frontier pricing tracker tracks.

The Cost-Per-Task Math#

Per-token rates understate what agent loops actually spend, so here is the same task across the field: 200K input / 20K output, standard rates, no cache.

Two takeaways. First, the gap between "cheap" and "frontier" collapsed: GPT-6 Sol's $0.60 uncached task is within 15% of Grok 4.7's $0.52 and half of Opus 5.5's $1.20, and it is the most capable coding model of the three by every published agent benchmark except the ones Anthropic disputes. Second, caching is where Opus 5.5 fights back: its 0.05x cache multiplier means a typical agent loop (over 90% of input tokens cached) pays $0.036 in cache reads versus Sol's identical $0.036, but Opus 5.5's uncached input at 2x Sol's rate. If your loops are cache-dominant and quality-sensitive, Opus 5.5 at $0.516 per task is the cheapest frontier-grade option with a published cache rate.

Decision Guide by Persona#

Coding agents on the OpenAI stack. GPT-6 Sol, unambiguously. It is the designated coding-and-agentic flagship, inherits Codex, the Responses API, and structured outputs, and its $10 output rate means output-heavy loops no longer need routing out of the flagship tier. If your workload is high-volume and simple, GPT-6 Luna at $0.10/$0.50 does the same job for a third of the input cost - see the budget tier comparison.

Long-horizon, quality-critical agent runs. Opus 5.5 is the strongest terminal-side story on the table (Terminal-Bench 4.0 66.4%) with the published cache economics to back it, and its fast mode at $8/$40 is a price-for-speed option alongside Grok's (2x output speed at 2x price). The caveat from early testers: stay on default effort levels, because max effort can burn the output ceiling.

Price-performance maximalists with router-friendly workloads. Grok 4.7 at $2/$6 is the cheapest flagship output rate on the market, with DeepSWE 71.0% (high effort) that matches Fable 5.1 and slots far above both GPT-6 Sol and Opus 5.5 on that axis. Its Terminal-Bench 4.0 score (37.6%) is the honest counterweight. Routing cheap-by-default with escalation handles exactly this shape of tradeoff - the routing strategies guide has the framework.

Anthropic shops. If you standardized on Claude for tooling and eval surface, note the pricing reality: Opus 5.5 at $4/$20 is 2.5x cheaper on input and output than Fable 5.1, and Anthropic's own claim is that it performs at Fable 5.1 level on most work. Buy the step down to Opus 5.5 unless your eval set shows the ceiling is what you pay for.

Cost floors. For any task where quality is secondary, the month's real news is GPT-6 Luna at $0.10/$0.50: it undercut DeepSeek on every axis, so the "cheapest frontier callable" label moved from open weights to a closed provider for the first time. Budget models built on the old DeepSeek math need a re-basing pass - the DeepSeek migration guide covers the September rename and rates.

When to Stay Put#

• Your cache is tuned to Anthropic. The 1-hour cache TTL and the new 0.05x multiplier on Opus 5.5 are real money in agent loops; switching to a provider without a published cache rate (Grok) forfeits that advantage blind.
• You are mid-migration. GPT-5.6-Sol at the $4/$20 promo through November 21 is still the safest OpenAI-side target if your tooling pins GPT-5.6-specific behavior; test GPT-6 Sol on a slice before rolling over.
• Benchmark disputes unresolved. The vendors' numbers disagree by 10+ points on the same benchmark names. If your workload is agentic and expensive, the cost of running your own golden-set eval is trivial next to a wrong platform bet.
• Max-effort behavior matters to you. The 128K output ceiling issue on Opus 5.5 at max effort (per Simon Willison's first pass) means teams that routinely push effort settings should test the ceiling before committing.

FAQ#

Which is cheaper: GPT-6 Sol or Claude Opus 5.5?#

GPT-6 Sol at $2/$10 per MTok versus Opus 5.5 at $4/$20 - Sol is 2x cheaper on both axes. On cached agent loops the gap narrows to $0.276 versus $0.516 per representative task, because Opus 5.5's cache reads ($0.20) match Sol's ($0.20) at a 0.05x multiplier versus Sol's 0.1x.

Is Grok 4.7 really $2/$6?#

Yes, verified September 26, 2026 from the official announcement: $2 per million input tokens and $6 per million output tokens, with a fast variant at double the output speed for double the price.

What is the difference between GPT-6 Astra, Sol, and Luna?#

Astra ($10/$50) is the max-capability model, used for long-horizon research runs and flagpole work; Sol ($2/$10) is the coding-and-agentic flagship and the sensible default for developers; Luna ($0.10/$0.50) is the high-volume workhorse. All three share a 1,050,000-token context window, and long-context rates rise to $20/$75, $4/$15, and $0.20/$0.75 respectively.

Is GPT-6 Sol better than GPT-5.6 Sol?#

It is the successor and replaces it as the coding-and-agentic flagship at half the price ($2/$10 versus $4/$20). GPT-5.6-Sol's promotional pricing runs at least through November 21, 2026, so the legacy tier remains available while teams migrate.

Does Claude Opus 5.5 have fast mode?#

Yes, at $8/$40 per MTok, available on the Claude API only (not Bedrock or other platforms), applied across the full context window. It is the same 2x-price structure as OpenAI's fast mode on the GPT-5.6 family.

Should I wait for Claude Sonnet 5.5 and Haiku 5.5?#

The 5.5 family is announced, not shipped: Anthropic's Opus 5.5 release notes say Sonnet 5.5 and Haiku 5.5 will follow "in the coming weeks" (verified September 26, 2026 on the pricing page, which lists neither yet). If you run Sonnet 5 at $2/$10 today, there is no announced successor price to wait on - Sonnet 5's rates are permanent.

Continue Reading#

• DeepSeek 4.1 Flash as a Daily Coding Model - cache math, peak-hour windows and what the HN thread says about the cost claims
• OpenAI DevDay 2026 Recap: What Shipped and What to Test - GPT-6.1 Sol at $2/$10, Ultrafast and the Decisions API, announced after this post
• Claude Opus 5.5 Release Guide: Fable 5.1-Level Coding at $4/$20 - the full benchmark table and the OpenCode setup
• Weekly Highlights: The Price War Reached the Frontier - the week in one ranked digest, from Enigma to driving tests
• Frontier Model API Pricing, September 2026 - the standing same-day-verified rate card across all providers
• Budget AI Coding Models Compared 2026 - what Luna and V4.1-Flash mean for the tier below
• AI Model Routing Strategies for Cost-Effective Coding - when routing between the tiers in this post pays