Long-running coding and knowledge work
Strong fit when the workload is reasoning-heavy, agentic and text/code centric, and the extra inference cost is justified by task value.
Open model reference ↗MODEL COMPARISON / VERIFIED 2026-09-26
Claude Opus 5.5
vs Gemini 3.8 Flash.
A source-first comparison for coding, agents and production AI. Official specifications, token economics, caching, batch processing, multimodal inputs and tool ecosystems are separated from vendor performance claims.
QUICK ANSWER
This is primarily a capability-depth vs cost-and-multimodality decision.
Claude Opus 5.5 is Anthropic’s current Opus model for long-running agentic coding and knowledge work, with a 128K output ceiling and adaptive thinking always enabled. Gemini 3.8 Flash is Google’s most intelligent stable Flash model, priced far lower in 2026 and accepting a broader mix of text, image, video, audio and PDF inputs. Both are designed for serious software engineering and autonomous workflows.
Cost-sensitive multimodal agents
Strong fit when workloads need broad media inputs, Google-native tools or significantly lower token economics at production volume.
Open model reference ↗Benchmark accepted task cost
Compare completed-task rate, retries, tool errors, reasoning tokens, cache hits, latency and human correction—not just a benchmark score or price per token.
OFFICIAL SPECIFICATIONS
Side-by-side facts.
| Model | Provider | Positioning | Context | Max output | Thinking | Modalities | Input | Cached | Output |
|---|---|---|---|---|---|---|---|---|---|
| Claude Opus 5.5claude-opus-5-5 | Anthropic | Long-running agentic coding and knowledge work | 1,000,000 | 128,000 | Adaptive thinking · always on · default medium | Text + image input · text output | $4.00 | $0.20 | $20.00 |
| Gemini 3.8 Flashgemini-3.8-flash | Long-horizon software engineering, autonomous agents and enterprise workflows | 1,048,576 | 65,536 | low · medium · high · default medium | Text + image + video + audio + PDF input · text output | $0.75* | $0.075* | $3.75* |
Claude rates are Anthropic’s current Standard API rates. Gemini rates marked * are Google’s introductory Standard paid prices through December 31, 2026; they change January 1, 2027.
PRICING
The token-price gap is large.
Gemini 3.8 Flash is substantially cheaper on current list pricing, but cost per accepted task can narrow or widen the difference depending on retries, effort, tools and caching.
100K input + 10K output
Claude Opus 5.5$0.6100K input + 10K output
Gemini 3.8 Flash$0.1125100K input + 10K output
10M input + 1M output
Claude Opus 5.5$6010M input + 1M output
Gemini 3.8 Flash$11.2510M input + 1M output
Gemini’s current rates are temporary
Google states that Standard pricing rises from $0.75 / $3.75 to $1.50 / $7.50 per million input/output tokens on January 1, 2027. Even at those higher rates, the headline token price remains below Opus 5.5’s current $4 / $20.
CACHE ECONOMICS
Both reward repeated context; Gemini’s read price is lower.
Prompt or context caching matters disproportionately for long-running agents that repeatedly reuse repository context, policy text, tools or large documents.
1M cached input + 100K output
Claude Opus 5.5$2.21M cached input + 100K output
Gemini 3.8 Flash$0.451M cached input + 100K output*
Claude caching
Opus 5.5 cache reads cost $0.20 per million tokens. Five-minute cache writes cost $5 and one-hour writes cost $8 per million tokens. The minimum cacheable prompt length is 512 tokens.
Gemini caching
Gemini 3.8 Flash context-cache reads cost $0.075 per million tokens through December 31, 2026 and $0.15 starting January 1, 2027. Google also charges cache storage per token-hour, so persistent-cache economics depend on both read volume and retention time.
BATCH & SPEED
Asynchronous cost vs premium latency.
Batch · 10M input + 1M output
Claude Opus 5.5$30Batch · 10M input + 1M output
Gemini 3.8 Flash$5.625Batch · 10M input + 1M output*
CLAUDE BATCH50% token discount
Anthropic’s Batch API halves Opus 5.5 input and output token rates, making it useful for asynchronous high-value jobs that do not require interactive latency.
GEMINI BATCH$0.375 / $1.875 in 2026
Google’s current Batch rates are half the introductory Standard token rates and rise to $0.75 / $3.75 on January 1, 2027.
CLAUDE FAST MODEUp to 2.5× output speed
Fast mode is a first-party Claude API research preview. It uses the same Opus 5.5 model at $8 input / $40 output per million tokens and is not available on partner cloud platforms.
CONTEXT & OUTPUT
Context capacity is similar; maximum output is not.
Gemini 3.8 Flash lists 1,048,576 input tokens, while Claude Opus 5.5 lists a 1 million-token context window. That difference is small enough that retrieval strategy, cache reuse and active working-set quality will usually matter more than the nominal capacity.
Claude Opus 5.5 supports up to 128,000 standard output tokens, roughly double Gemini 3.8 Flash’s 65,536. Anthropic additionally offers up to 300K output in the Batch API under a beta feature. Large output limits can matter for code generation, long reports and artifact-heavy workflows.
Neither number should be treated as a target. Sending or generating huge token volumes increases cost and can make agents harder to evaluate and debug.
CODING
Both are explicitly designed for serious software engineering.
Long-running agentic coding
Anthropic positions Opus 5.5 for multihour coding sessions, large refactors, audits and complex systems work where an agent must stay coherent across many tool calls.
Long-horizon software engineering
Google positions 3.8 Flash for real-world coding, complex multi-file refactoring and deterministic tool execution while retaining the Flash family’s cost orientation.
Use the same repository and harness
Compare accepted patches, test pass rates, retries, human corrections, token use and elapsed time. Vendor launch benchmarks are useful signals but not interchangeable scoreboards.
AGENTS & TOOLS
The ecosystems are powerful in different ways.
CLAUDE · TOOL LOOPSLong-running agent workflows
Opus 5.5 supports server-side and client-side tools, task budgets, prompt caching, Files API and agent-oriented conversation controls.
CLAUDE · COMPUTER USESupported with current toolset
Anthropic supports computer-use workflows, with updated tool requirements on Claude API and Google Cloud for Opus 5.5.
CLAUDE · PROGRESS UPDATESThinking-block display controls
Applications can surface progress between tool calls when configured to display the relevant progress-update content instead of leaving long agents silent.
GEMINI · GROUNDINGGoogle Search + Maps
3.8 Flash supports Search and Maps grounding for workflows that need current web or location evidence.
GEMINI · EXECUTIONCode execution + computer use
Google lists code execution, function calling, file search, URL context and computer use in preview on the stable model.
GEMINI · MANAGED AGENTSDefault Antigravity model
Google’s latest-model guidance says 3.8 Flash is the default model for its managed Antigravity agent and SDK.
THINKING
Both default to medium, but the control model differs.
Claude Opus 5.5 uses adaptive thinking that is always on. Developers control depth with the effort parameter, and Anthropic documents medium as the default. Thinking cannot be disabled on this model.
Gemini 3.8 Flash supports low, medium and high thinking levels, also defaulting to medium. Google notes that difficult long-running tasks may deliberately consume more reasoning tokens as the model takes smaller steps and verifies intermediate results.
For both models, benchmark at the lowest setting that reliably clears your quality bar. Thinking tokens contribute to output cost, so higher reasoning can materially affect the economics of long agent workflows.
MULTIMODAL
Gemini 3.8 Flash has the broader direct input surface.
Text + image at the model layer
Anthropic’s model specification lists text and images as inputs and text as output. The broader Claude platform also supports Files API, PDF and vision workflows.
Text + image + video + audio + PDF
Google explicitly lists all five input types on the stable 3.8 Flash endpoint, which can reduce preprocessing complexity in media-heavy workflows.
Separate model families
Standard Gemini 3.8 Flash does not support the Live API; Google provides dedicated 3.8 Live models. Opus 5.5 is not a native audio-to-audio model either.
DEPLOYMENT
Cloud and platform fit can outweigh base-model differences.
Native Anthropic API
Opus 5.5 is active on the Claude API and also available through Amazon Bedrock, Google Cloud, Microsoft Foundry and Claude Platform on AWS.
Gemini API + AI Studio
Gemini 3.8 Flash is a stable GA model in the Gemini API and Google AI Studio with Standard, Batch, Flex and Priority consumption options.
Vertex AI and managed agents
3.8 Flash fits naturally in Google Cloud environments that want Vertex AI, Search/Maps grounding or Google’s managed agent stack.
WHEN TO CHOOSE
Choose by workload, not by a universal winner.
High-value long-running coding
Consider Opus when sustained reasoning, large output headroom and Anthropic’s agent workflow behavior justify the higher inference cost.
Complex text-heavy knowledge work
It is a strong candidate for research, professional analysis and long document workflows where quality per completed task matters more than minimum token price.
High-volume production agents
Its current token economics are attractive when many agent runs need real reasoning and tools without premium per-token spend.
Media-rich workflows
Use it when video, audio, PDFs, images and text need to enter the same reasoning workflow directly.
LIMITS & CAVEATS
What can make a simple comparison wrong.
01Gemini’s 2026 prices are introductory.
They double on January 1, 2027, so long-term cost planning should include both periods.
02Opus thinking cannot be disabled.
Adaptive thinking is always on, so cost and latency behavior differs from models that allow a true no-thinking route.
03Cache examples exclude storage time.
Gemini charges a separate token-hour storage fee for context caching; actual savings depend on reuse frequency and retention duration.
04Fast mode is not free speed.
Claude Fast mode doubles standard Opus 5.5 token rates and is available only as a research preview on the first-party Claude API.
05Tool charges and cloud economics differ.
Search, Maps, data residency, managed agents and cloud platform pricing can change total workflow cost beyond model tokens.
06Model APIs are not consumer apps.
This page compares model/platform capabilities, not the complete Claude app versus Gemini app experience.
OFFICIAL SOURCES
Anthropic · Claude Opus 5.5 model page↗Anthropic · What’s new in Claude Opus 5.5↗Anthropic · Claude pricing↗Anthropic · Fast mode↗Google AI · Gemini 3.8 Flash model page↗Google AI · What’s new in Gemini 3.8 Flash↗Google AI · Gemini API pricing↗Google AI · Models overview↗QUICK ANSWERS
Which is cheaper, Claude Opus 5.5 or Gemini 3.8 Flash?
At current Standard API rates through December 31, 2026, Gemini 3.8 Flash has much lower headline token prices: $0.75 input and $3.75 output per million tokens versus $4 and $20 for Claude Opus 5.5. Google states that Gemini 3.8 Flash Standard pricing doubles to $1.50 input and $7.50 output on January 1, 2027.
Which has the larger context window?
Gemini 3.8 Flash lists 1,048,576 input tokens, while Claude Opus 5.5 lists a 1 million-token context window. The difference is small. Claude Opus 5.5 has the larger standard maximum output at 128,000 tokens versus 65,536 for Gemini 3.8 Flash.
Which model supports more input modalities?
Gemini 3.8 Flash explicitly supports text, image, video, audio and PDF input. Claude Opus 5.5's model specification lists text and image input with text output, while Anthropic's broader platform also supports Files API and PDF workflows.
How do thinking controls differ?
Claude Opus 5.5 uses adaptive thinking that is always on and defaults to medium effort. Gemini 3.8 Flash supports low, medium and high thinking levels and also defaults to medium.
Which is better for coding?
Both are explicitly designed for serious software engineering. Anthropic positions Opus 5.5 for long-running agentic coding; Google positions Gemini 3.8 Flash for long-horizon software engineering and complex multi-file refactoring. A reliable decision requires the same repository, tests, tools and acceptance criteria.
Which is better for AI agents?
Both support multi-step tool workflows. Opus 5.5 is designed for long-running agentic coding and supports server-side and client-side tools through Anthropic's platform. Gemini 3.8 Flash supports function calling, code execution, file search, Search grounding, Maps grounding, URL context and computer use in preview. Platform fit and permissions often matter more than a generic agent benchmark.
How do prompt caching costs compare?
Claude Opus 5.5 cache reads cost $0.20 per million tokens. Gemini 3.8 Flash context cache reads cost $0.075 per million tokens through December 31, 2026 and $0.15 starting January 1, 2027, with a separate cache-storage charge.
How does batch pricing compare?
Anthropic's Batch API provides a 50% discount, making Opus 5.5 batch token rates effectively $2 input and $10 output per million tokens. Gemini 3.8 Flash Batch pricing is $0.375 input and $1.875 output through December 31, 2026, rising to $0.75 and $3.75 on January 1, 2027.
Does Claude Opus 5.5 have a faster inference mode?
Yes. Anthropic offers Fast mode as a research preview on the first-party Claude API. It can deliver up to 2.5x higher output tokens per second and costs $8 input and $40 output per million tokens.
Does either model support real-time voice?
The standard Gemini 3.8 Flash model does not support the Live API; Google provides separate Gemini 3.8 Live models. Claude Opus 5.5's model specification lists text and image input and text output, not native audio-to-audio interaction.