Claude Sonnet 5 vs GPT-5.5
Anthropic's new mid-tier against OpenAI's shipping flagship — a 2.5-3x price gap, matching 1M contexts, and two different definitions of "agentic."
Claude Sonnet 5 vs GPT-5.5: side-by-side
| Claude Sonnet 5 | GPT-5.5 "Spud" | |
|---|---|---|
| Maker | Anthropic | OpenAI |
| Released | 30 June 2026 | 23 April 2026 |
| Tier | Mid-tier (below Opus 4.8) | Flagship |
| Context window | 1M tokens (default & max) | 1M tokens (400K in Codex CLI) |
| Max output | 128K tokens | Not specified |
| API price (per 1M) | $2 / $10 intro · $3 / $15 from Sep 2026 | $5 / $30 |
| Built for | Agentic work at production cost | Agentic coding, computer use, deep research |
| Standout | Finishes tasks, self-checks · default on claude.ai Free/Pro | 82.7% Terminal-Bench 2.0 · Codex integration |
Where Claude Sonnet 5 wins
Price, decisively. During the intro window Sonnet 5 costs $2/$10 against GPT-5.5's $5/$30 — 60% less on input, 67% less on output. Even at the September rate card ($3/$15) the output-token gap stays 2x. For any high-volume loop, that compounds fast.
Task completion. The consistent early-access report is that Sonnet 5 is much more agentic than its predecessors: it finishes complex tasks earlier Sonnets stopped short on, and checks its own output unprompted. And its 1M context is the default — no premium tier, no CLI carve-out.
Where GPT-5.5 wins
Published peak numbers. GPT-5.5 posts 82.7% on Terminal-Bench 2.0 and 73.1% on Expert-SWE — the strongest published agentic-coding scores of the shipping generation. Sonnet 5 launched without a comparable public benchmark table, so on paper GPT-5.5 remains the measurable leader.
Ecosystem. GPT-5.5 is woven into Codex and OpenAI's computer-use stack. If your workflow is already there, switching costs are real. Note OpenAI is also previewing GPT-5.6, whose Terra variant claims GPT-5.5 performance at half the price — worth watching before committing long-term.
Price comparison
| Model | Input (per 1M) | Output (per 1M) |
|---|---|---|
| Claude Sonnet 5 (intro, to 31 Aug 2026) | $2.00 | $10.00 |
| Claude Sonnet 5 (standard) | $3.00 | $15.00 |
| GPT-5.5 (Thinking) | $5.00 | $30.00 |
Key takeaway
This is a flagship-vs-mid-tier match-up, and that's exactly why it matters: if a mid-tier model finishes your agentic tasks reliably at a third of the price, the flagship premium needs to be earning its keep on your specific workload — not on a leaderboard.
Which should you use?
- High-volume production agents → Claude Sonnet 5 — the cost math dominates.
- Peak published agentic-coding performance → GPT-5.5.
- Codex-centered workflows → GPT-5.5.
- Long-document / whole-codebase work on a budget → Claude Sonnet 5 (1M context by default).
- Absolute frontier regardless of cost → neither — see Claude Opus 4.8 or Claude Fable 5.
Full Claude Sonnet 5 overview Full GPT-5.5 overview
Frequently asked questions
Is Claude Sonnet 5 better than GPT-5.5?
They target different points. GPT-5.5 has the strongest published agentic-coding scores; Sonnet 5 is praised for finishing complex agentic tasks and self-checking at 2.5-3x lower cost. For price-performance, Sonnet 5; for peak published benchmarks, GPT-5.5.
Which is cheaper?
Claude Sonnet 5 by a wide margin: $2/$10 at intro pricing (through 31 Aug 2026), then $3/$15 — versus GPT-5.5's $5/$30.
Which has a bigger context window?
Both offer 1M tokens. GPT-5.5 drops to 400K inside the Codex CLI; Sonnet 5's 1M is the default everywhere.
Which should I use for agents?
GPT-5.5 for peak benchmark performance and Codex integration; Sonnet 5 when the loop runs at volume and cost decides.