Claude Opus Fast Mode Deprecated: Complete Migration Guide Before the July 24 Hard Error

Anthropic deprecated fast mode for Claude Opus 4.7 on June 25, 2026. On July 24, 2026, Opus 4.7 fast mode requests will return a hard error — no silent fallback, no degraded response, just a failure. If your codebase sends fast_mode: true or uses the /fast toggle in Claude Code targeting Opus 4.7, you have roughly three weeks to migrate.

This guide walks through the exact steps: find every fast mode reference in your codebase, understand the two different failure modes between Opus 4.6 and 4.7, pick the right alternative (effort levels, Opus 4.8 fast mode, or standard inference), and configure fallback routing to stay resilient.

We route OpenAI-compatible requests through configured providers and support provider/model routing and fallback where the live product path supports it. We do not claim zero downtime or universal model support. Every date and pricing figure below is sourced from Anthropic's official documentation at retrieval time.

30-second answer

• Fast mode on Opus 4.7 was deprecated June 25, 2026. Hard error deadline: July 24, 2026 (Claude Code fast mode docs, retrieved 2026-07-02).
• Fast mode on Opus 4.6 was already silently removed — calls succeed but run at standard speed, with no error.
• Opus 4.8 fast mode remains fully supported at $10/$50 per MTok input/output (Anthropic pricing, retrieved 2026-07-02).
• Effort levels (low, medium, high, xhigh, max) are the recommended alternative for speed/quality tradeoffs without the fast mode cost premium (Effort docs, retrieved 2026-07-02).
• Migrate in three steps: audit your codebase, pick an alternative, and configure fallback routing.

1. Swap three values, not three SDKs. Change api_key, base_url, and model in the existing OpenAI client. Keep your request/response code unchanged.
2. Map model IDs explicitly. The target provider's model id is almost never identical to the OpenAI id. Keep a single dict of { openai_id: target_id } outside business logic.
3. Verify streaming format. SSE chunks must follow the OpenAI data: {...} + data: [DONE] contract. Test one streaming call before moving production traffic.
4. Check rate-limit headers. Some providers omit x-ratelimit-* headers. Add a wrapper that defaults safely when headers are absent.
5. Keep a rollback path. Ship the swap behind a feature flag, run both endpoints in shadow for 24 hours, then cut over.

What is fast mode, and why is it being removed?

Fast mode is not a separate model — it is a configuration that prioritizes latency over cost efficiency on the same Claude Opus model. When enabled, Opus delivers responses up to 2.5x faster at a significantly higher per-token cost.

Anthropic introduced fast mode as a research preview. As effort levels matured (particularly xhigh on Opus 4.7 and 4.8), the speed gains from lowering effort largely overlap with what fast mode offers, while giving developers finer-grained control. The Opus 4.7 deprecation follows Opus 4.6's silent removal, consolidating the speed dial into the effort parameter.

Key point: fast mode and effort levels are complementary but distinct mechanisms. Fast mode reduces latency at the infrastructure level (same quality, higher cost). Effort levels reduce thinking depth (faster responses, potentially lower quality on hard tasks). You can combine both — but after July 24, you can only combine them on Opus 4.8.

Two models, two failure modes

This is the critical distinction most migration guides miss:

Source: Claude Code fast mode docs, retrieved 2026-07-02.

Why this matters: If you are on Opus 4.6 with fast mode enabled, your code already runs in standard mode without errors — you are paying standard rates but may not realize fast mode is not active. On Opus 4.7, the behavior flip on July 24 is abrupt: working today, hard error tomorrow.

Audit your codebase: find every fast mode reference

Before choosing a migration path, find every place fast mode is referenced. Here are grep patterns for the most common SDKs and configurations:

Python SDK

# Direct API parameter
grep -rn 'fast_mode' --include="*.py" .

# Anthropic Python SDK client configuration
grep -rn 'FastMode\|fast_mode\|\"fast\"\|speed.*mode' --include="*.py" .

# Environment variables
grep -rn 'ANTHROPIC_FAST_MODE\|CLAUDE_FAST_MODE' --include="*.py" --include="*.env" --include="*.yaml" --include="*.toml" .

Node.js / TypeScript SDK

# Direct parameter
grep -rn 'fastMode\|fast_mode\|\"fast\"' --include="*.ts" --include="*.js" --include="*.mjs" .

# Configuration files
grep -rn 'fastMode\|fast_mode' --include="*.json" --include="*.yaml" --include="*.yml" .

Claude Code CLI configuration

# User settings
grep -rn 'fastMode' ~/.claude/ 2>/dev/null

# Project-level settings
find . -name ".claude*" -exec grep -l 'fastMode\|fast_mode' {} \;

# Check if /fast was toggled (persists across sessions by default)
grep -rn 'fastMode' ~/.config/claude-code/ 2>/dev/null

Go SDK

grep -rn 'FastMode\|fast_mode\|WithFastMode' --include="*.go" .

What to look for: any parameter, environment variable, or configuration key that enables fast mode. Pay special attention to CI/CD pipelines and Docker configurations where environment variables may set fast mode.

Choose your migration path

Option 1: Upgrade to Opus 4.8 fast mode (keep the speed)

If latency is critical and budget is not the primary concern, move to Opus 4.8 fast mode. The pricing actually improved:

Source: Claude Code fast mode docs, retrieved 2026-07-02.

Code change (Python):

# Before: Opus 4.7 with fast mode
response = client.messages.create(
    model="claude-opus-4-7-20260416",
    # fast_mode=True,  # DEPRECATED — hard error after July 24
    max_tokens=4096,
    messages=[{"role": "user", "content": prompt}],
)

# After: Opus 4.8 with fast mode
response = client.messages.create(
    model="claude-opus-4-8-20260528",
    # fast_mode=True,  # Supported on 4.8
    max_tokens=4096,
    messages=[{"role": "user", "content": prompt}],
)

Claude Code CLI:

# Switch model, keep fast mode
/model opus
# If already on 4.7, Claude Code v2.1.154+ defaults to 4.8 for fast mode
/fast

Trade-off: Opus 4.8 has a 200K context window (vs 1M on 4.7 standard). For most fast mode use cases (interactive coding, rapid iteration), 200K is sufficient. If you need 1M context with speed, see Option 2.

Option 2: Use effort levels (cost-efficient speed)

Effort levels give you a speed/quality dial without the fast mode price premium. Since Opus 4.7, five levels are available:

Source: Effort docs, retrieved 2026-07-02.

Recommended mapping for fast mode users:

• Interactive debugging / rapid iteration → medium effort on Opus 4.7 or 4.8. Comparable speed to fast mode for straightforward tasks, at standard pricing.
• Complex coding with speed → xhigh effort on Opus 4.8. Anthropic recommends xhigh as the starting point for coding and agentic work on Opus 4.7+.
• Maximum speed, lower quality acceptable → low effort. Significant token savings, suitable for subagents or classification.

Code change (Python):

# Before: Opus 4.7 with fast mode
response = client.messages.create(
    model="claude-opus-4-7-20260416",
    # fast_mode=True,
    max_tokens=4096,
    messages=[{"role": "user", "content": prompt}],
)

# After: Opus 4.7 with medium effort (speed-focused)
response = client.messages.create(
    model="claude-opus-4-7-20260416",
    max_tokens=4096,
    effort="medium",  # Faster responses, standard pricing
    messages=[{"role": "user", "content": prompt}],
)

Key advantage: effort levels work on all supported models, not just Opus. You can use the same effort parameter on Sonnet 5 ($2/$10 introductory pricing through August 31), which is often fast enough for interactive work at a fraction of the cost.

Option 3: Remove fast mode, stay on standard Opus

If fast mode was enabled opportunistically and latency is not a hard requirement:

# Just remove the fast mode parameter — everything else stays the same
response = client.messages.create(
    model="claude-opus-4-7-20260416",
    max_tokens=4096,
    messages=[{"role": "user", "content": prompt}],
)

Standard Opus 4.7 at high effort (the default) already outperforms Opus 4.6 at max effort on coding benchmarks. The model got faster between versions — you may not need fast mode at all.

Cost comparison: fast mode vs alternatives

Sources: Anthropic pricing, Claude Code fast mode docs, retrieved 2026-07-02.

Note: Opus 4.7 and later models use a newer tokenizer that produces approximately 30% more tokens for the same text compared to Opus 4.5 and earlier. Factor this into cost projections when comparing across model generations.

Rollback strategy: fallback routing during migration

Rather than a hard cutover, route traffic through a fallback chain that gracefully handles the transition:

Fallback chain for fast mode users:

1. Primary: Opus 4.8 with fast mode (if you need guaranteed speed)
2. First fallback: Opus 4.7 standard with xhigh effort (if 4.8 is overloaded)
3. Second fallback: Sonnet 5 with high effort (cost-efficient alternative)

We support provider/model routing and fallback when the live product path supports it. This means you can configure a model priority list, and if the primary model returns an error (including the July 24 fast mode hard error on Opus 4.7), requests automatically route to the next model in the chain.

Why this matters for July 24: if you miss a fast mode reference in your codebase and it fires against Opus 4.7 after the deadline, a fallback chain prevents a total outage. The request fails on 4.7, falls through to 4.8 or Sonnet 5, and your user gets a response instead of an error.

For detailed fallback configuration, see our LLM API Fallback Routing Guide.

Claude Code specific migration

If you use Claude Code (CLI), the migration is straightforward:

1. Check your version: claude --version. You need v2.1.154+ for Opus 4.8 fast mode default.
2. Check current fast mode state: type /fast — it will show whether fast mode is on or off.
3. If on Opus 4.7 with fast mode:
   • Update Claude Code: claude update
   • Toggle off: /fast
   • Switch model: /model → select opus (4.8 is the default on v2.1.154+)
   • Re-enable if needed: /fast (now targets 4.8)
4. Check persistent settings: look for "fastMode": true in your settings file. Run /fast to toggle off, or edit the settings file directly.

Organization admins (Team/Enterprise):

• Fast mode is disabled by default for Team/Enterprise. If you previously enabled it, no action needed — users on Opus 4.8 continue working.
• If your availableModels allowlist excludes Opus 4.8, users cannot migrate fast mode. Update the allowlist to include claude-opus-4-8.

Migration timeline and checklist

Pre-deployment checklist:

• Searched codebase for fast_mode, fastMode, FastMode, /fast references
• Checked environment variables: ANTHROPIC_FAST_MODE, CLAUDE_FAST_MODE
• Checked Claude Code user settings and project settings
• Checked CI/CD pipeline configurations and Docker environment variables
• Selected migration path: Opus 4.8 fast mode, effort levels, or standard mode
• Configured fallback routing to handle residual fast mode errors
• Tested in staging with the new configuration
• Updated SDK to latest version (Python ≥ 0.52.x, Node ≥ 0.52.x for effort support)

FAQ

Q: Will fast mode ever come back on Opus 4.7? A: No. Anthropic's deprecation notice is final — fast mode on Opus 4.7 will be removed on July 24, 2026. The feature continues on Opus 4.8.

Q: I use fast mode on Opus 4.6 — do I need to do anything? A: No immediate action needed. Fast mode on Opus 4.6 was already silently removed — your calls succeed but run at standard speed. You are not paying fast mode rates. Consider updating to Opus 4.8 if you need the speed.

Q: Is fast mode available on Bedrock, Vertex AI, or Azure Foundry? A: No. Fast mode is only available through the Anthropic Console API and Claude subscription plans (Pro/Max/Team/Enterprise). It is not available on Amazon Bedrock, Google Vertex AI, or Microsoft Azure Foundry.

Q: Can I combine fast mode and effort levels? A: Yes, on Opus 4.8. You can set fast_mode: true and effort: "medium" for maximum speed on straightforward tasks. This is not possible on Opus 4.7 after July 24.

Q: What if I need 1M context with fast speed? A: Opus 4.8 fast mode has a 200K context window. Opus 4.7 standard mode (with medium or high effort) retains the full 1M context. If you need 1M context and speed, use Opus 4.7 with a lower effort level.

Internal links

• Claude Opus 4.7 model page — full model details, pricing, and capabilities
• Claude Opus 4.8 model page — the recommended fast mode target
• Anthropic provider page — all Claude models available through TheRouter
• Anthropic Deprecation Cadence Migration Guide — broader deprecation patterns and planning
• LLM API Fallback Routing Guide — how to configure multi-model fallback chains
• Claude Sonnet 5 vs Opus 4.8 Routing Cost Comparison — cost-optimized model selection

---

Sources cited in this article: Claude Code fast mode docs (retrieved 2026-07-02), Anthropic pricing (retrieved 2026-07-02), Effort docs (retrieved 2026-07-02), Model deprecations (retrieved 2026-07-02).