Claude Sonnet 4.6 vs Opus 4.6: 1M Token Context Is Now Standard — Migration Guide
April 2, 2026 · 7 min read
TL;DR
The 1M token beta header (context-1m-2025-08-07) retires April 30, 2026 for Sonnet 4.5 and Sonnet 4. Migrate to Claude Sonnet 4.6 (GA since Feb 17) or Claude Opus 4.6 (GA since Feb 5) — both have 1M context by default. Remove the beta header, update your model ID, done. Message Batches API max_tokens raised to 300K on Sonnet 4.6. Sonnet 4.6 at $3/$15 handles 70% of use cases; Opus 4.6 at $5/$25 for deep reasoning tasks.
Anthropic shipped 1M token context windows as a general availability feature in early 2026, graduating both Claude Sonnet 4.6 and Claude Opus 4.6 out of beta. If your codebase still uses the context-1m-2025-08-07 beta header on older models, you have until April 30, 2026 to migrate. Here is everything you need to know.
What Changed and When
| Event | Date | Action Required |
|---|---|---|
| Claude Opus 4.6 GA with 1M context | February 5, 2026 | Optional upgrade for reasoning-heavy workloads |
| Claude Sonnet 4.6 GA with 1M context | February 17, 2026 | Recommended migration target for most developers |
| Message Batches API max_tokens raised to 300K | February 17, 2026 | No action needed — automatic on Sonnet 4.6 |
| Beta header retires for Sonnet 4.5 + Sonnet 4 | April 30, 2026 | Migrate before this date or requests fail |
Sonnet 4.6 vs Opus 4.6: Which Model for Which Task
| Feature | Sonnet 4.6 | Opus 4.6 |
|---|---|---|
| Release date | February 17, 2026 | February 5, 2026 |
| Context window | 1,000,000 tokens (GA) | 1,000,000 tokens (GA) |
| Input price | $3 / million tokens | $5 / million tokens |
| Output price | $15 / million tokens | $25 / million tokens |
| Developer preference | 70% of developers | 30% of developers |
| Best for | Coding, summarization, agentic tasks, most production workloads | Deep research synthesis, complex multi-step reasoning, strategic analysis |
| Message Batches max_tokens | 300,000 | 300,000 |
How to Migrate: 3-Step Code Update
For most developers using the beta 1M context header, migration is a two-line change. Here is the exact diff:
Step 1: Remove the beta header
// Remove this:
headers: { 'anthropic-beta': 'context-1m-2025-08-07' }
// No replacement needed — 1M context is now default on 4.6 models
Step 2: Update the model ID
// Before:
model: "claude-sonnet-4-5"
// After (choose one):
model: "claude-sonnet-4-6" // Most use cases
model: "claude-opus-4-6" // Deep reasoning workloads
Step 3: Update Message Batches max_tokens (optional)
// If you use the Message Batches API, you can now set:
max_tokens: 300000 // Previously capped at 8192 on older models
What 1M Tokens Actually Enables
One million tokens is approximately 750,000 words — roughly the entire text of the Harry Potter series (1.1M words). In practice, this enables:
- Full codebase analysis: Load an entire repository (300–500 files) into a single context and ask architectural questions
- Legal document review: Process 500-page contracts, SEC filings, or regulatory documents in one pass
- Research synthesis: Feed 50–100 research papers and ask for synthesis, gaps, and contradictions
- Long conversation memory: Maintain context across thousands of turns without external memory systems
- Video transcript analysis: Process 10+ hours of meeting transcripts or lecture recordings at once
Which Model Should You Choose?
The decision comes down to task type, not token count — both models have identical 1M context windows.
Choose Sonnet 4.6 for:
- Production applications where latency and cost matter
- Coding, code review, and software architecture tasks
- Document summarization and data extraction
- Agentic workflows and tool use
- Any task where you currently use Sonnet 4.5
Choose Opus 4.6 for:
- Multi-step research tasks requiring extended reasoning chains
- Strategic business analysis where reasoning quality outweighs cost
- Complex problem decomposition across very long documents
- Nuanced judgment tasks where Sonnet produces inconsistent results
Use Claude's 1M Context Through Happycapy
Upload entire documents, codebases, and research collections — Happycapy leverages the full 1M token window for complex analysis and synthesis.
Try Happycapy →Frequently Asked Questions
When does the Claude 1M token beta expire?
The beta header context-1m-2025-08-07 for Claude Sonnet 4.5 and Claude Sonnet 4 expires April 30, 2026. After that date, requests using that header will be rejected. Sonnet 4.6 and Opus 4.6 have 1M context as a GA feature — no header required.
What is the difference between Claude Sonnet 4.6 and Opus 4.6?
Both support 1M token context. Sonnet 4.6 ($3/$15 per million tokens) is faster and covers 70% of developer use cases. Opus 4.6 ($5/$25 per million tokens) delivers deeper multi-step reasoning for complex research and analysis tasks.
How do I migrate from the Claude 1M beta to Sonnet 4.6?
Remove the anthropic-beta: context-1m-2025-08-07 header and update your model ID to claude-sonnet-4-6. No other changes required — 1M context is the default maximum.
What is the max_tokens limit on Message Batches API with Sonnet 4.6?
With Claude Sonnet 4.6 on the Message Batches API, max_tokens is raised to 300,000 output tokens per request — up from the previous 8,192 limit on older models. This enables batch processing of long-form documents significantly more efficiently.
Sources
- • Anthropic API documentation: Claude Sonnet 4.6 and Opus 4.6 release notes, February 2026
- • Anthropic developer changelog: 1M context GA announcement, February 2026
- • Anthropic Message Batches API documentation: max_tokens update, February 2026
- • Anthropic beta header deprecation notice: context-1m-2025-08-07 retirement, April 30, 2026