Documentation-based comparison
Claude Sonnet 5.5 versus Gemini 3.8 Flash
Compare documented scope and conditions. Unknowns remain unknown; different billing units do not establish a cost winner.
What the evidence answers
A reading of reviewed official documentation for Claude Sonnet 5.5 and Gemini 3.8 Flash. It is not a hands-on test, a ranking or a recommendation of one product.
Price
- Claude Sonnet 5.5 Usage-based API pricing
- Gemini 3.8 Flash Usage-based API pricing
These prices use differently defined usage units. Read each with its own unit and conditions; they do not add up to one total or a cheaper product.
Documented for both
- Provider
- Claude Sonnet 5.5 Anthropic
- Gemini 3.8 Flash Google
- API model identifier
- Claude Sonnet 5.5 claude-sonnet-5-5
- Gemini 3.8 Flash gemini-3.8-flash
- Modalities
- Claude Sonnet 5.5 Text and image input; text output
- Gemini 3.8 Flash Text, image, video, audio and PDF input; text output
- Context window
- Claude Sonnet 5.5 1M tokens in the context window
- Gemini 3.8 Flash 1,048,576 input tokens (not a shared context-window measurement)
- Maximum output
- Claude Sonnet 5.5 128K output tokens (standard API)
- Gemini 3.8 Flash 65,536 output tokens
- Input token rate
- Claude Sonnet 5.5 2 USD per million base input tokens
- Gemini 3.8 Flash 0.75 USD per million input tokens
- Output token rate
- Claude Sonnet 5.5 10 USD per million output tokens
- Gemini 3.8 Flash 3.75 USD per million output tokens, including thinking
- Availability
- Claude Sonnet 5.5 Active model; released 28 September 2026.
- Gemini 3.8 Flash Stable model alias; documentation lists a September 2026 update.
Limits to check
- Claude Sonnet 5.5 The standard output ceiling is 128K tokens; the documented 300K batch option requires a separate beta header. Thinking and tool behavior are model-specific.
- Gemini 3.8 Flash The documented input limit is 1,048,576 tokens and output limit is 65,536. The standard paid rates shown here expire after 31 December 2026.
Not verified yet
Every compared requirement has evidence for at least one.
Not verified means our reviewed sources do not establish it. It does not mean a product lacks the capability or that it costs nothing.
Next steps
| Requirement | Claude Sonnet 5.5 | Gemini 3.8 Flash |
|---|---|---|
| Pricing | Usage-based API pricing | Usage-based API pricing |
| Who it is for | An Anthropic Claude model with text and image inputs and text output. Verified Oct 18, 2026 · Claude Sonnet 5.5: official API documentation | A Google Gemini model accepting text, images, video, audio and PDFs, with text output. Verified Oct 18, 2026 · Gemini 3.8 Flash: official API documentation |
| Coverage limits | The standard output ceiling is 128K tokens; the documented 300K batch option requires a separate beta header. Thinking and tool behavior are model-specific. Verified Oct 18, 2026 · Claude Sonnet 5.5: official API documentation | The documented input limit is 1,048,576 tokens and output limit is 65,536. The standard paid rates shown here expire after 31 December 2026. Verified Oct 18, 2026 · Gemini 3.8 Flash: official API documentation |
| Provider | Anthropic Provider identity is linked to the separate Anthropic Claude API entry. Verified Oct 18, 2026 · Claude Sonnet 5.5: official API documentation | Google Provider identity is linked to the separate Google Gemini API entry. Verified Oct 18, 2026 · Gemini 3.8 Flash: official API documentation |
| API model identifier | claude-sonnet-5-5 Verified Oct 18, 2026 · Claude Sonnet 5.5: official API documentation | gemini-3.8-flash Verified Oct 18, 2026 · Gemini 3.8 Flash: official API documentation |
| Modalities | Text and image input; text output Verified Oct 18, 2026 · Claude Sonnet 5.5: official API documentation | Text, image, video, audio and PDF input; text output Verified Oct 18, 2026 · Gemini 3.8 Flash: official API documentation |
| Context window | 1M tokens in the context window Verified Oct 18, 2026 · Claude Sonnet 5.5: official API documentation | 1,048,576 input tokens (not a shared context-window measurement) Verified Oct 18, 2026 · Gemini 3.8 Flash: official API documentation |
| Maximum output | 128K output tokens (standard API) Verified Oct 18, 2026 · Claude Sonnet 5.5: official API documentation | 65,536 output tokens Verified Oct 18, 2026 · Gemini 3.8 Flash: official API documentation |
| Input token rate | 2 USD per million base input tokens Standard base input rate for Claude Sonnet 5.5. Prompt cache writes/reads and batch processing have separate rates; tools, service tier and taxes can change the total. Verified Oct 18, 2026 · Claude Sonnet 5.5: official API documentation | 0.75 USD per million input tokens Gemini 3.8 Flash Standard paid tier through 31 December 2026; USD 1.50 from 1 January 2027. Cache storage, grounding, other service tiers and taxes are separate. Verified Oct 18, 2026 · Gemini 3.8 Flash: official API documentation |
| Output token rate | 10 USD per million output tokens Standard output rate for Claude Sonnet 5.5. Compare the exact consumption option; the batch discount is separate. Verified Oct 18, 2026 · Claude Sonnet 5.5: official API documentation | 3.75 USD per million output tokens, including thinking Gemini 3.8 Flash Standard paid tier through 31 December 2026; USD 7.50 from 1 January 2027. Other service tiers, cache storage, grounding and taxes are separate. Verified Oct 18, 2026 · Gemini 3.8 Flash: official API documentation |
| Availability | Active model; released 28 September 2026. Vendor lifecycle status checked on 18 October 2026; account and platform eligibility require confirmation. Verified Oct 18, 2026 · Claude Sonnet 5.5: official API documentation | Stable model alias; documentation lists a September 2026 update. Documentation status, not an account-specific access guarantee. Verified Oct 18, 2026 · Gemini 3.8 Flash: official API documentation |
| Coverage note | Official documentation checked on 18 October 2026; no hands-on test. | Official documentation checked on 18 October 2026; no hands-on test. |