How can we ensure that context is not lost and costs are not doubled after switching APIs in Claude Code?

Many teams encounter two frustrating issues when switching Claude Code API relay services or configuring Claude API proxies.txt

Many teams, when switching Claude Code API relay services or configuring Claude API proxies, often run into two nasty surprises: conversational context mysteriously breaks, and token bills quietly spike. When the model seems to become sluggish, it’s usually because the relay service has dropped session caches or broken routing logic — domain changes, cache key errors, and erratic route drifting are the usual culprits behind the scenes.

This article draws on real-world experience with Claude API gateway deployments to show you how to keep sessions uninterrupted, caches valid, and costs under control.

Does switching relay services for Claude Code cause chat history to disappear?

Switching relays does not directly erase chat history. Whether context remains coherent depends critically on where conversation data is stored.

• If conversation history is saved locally by the application, and each request carries the full context explicitly, then simply changing ANTHROPIC_BASE_URL to point to the new address will leave all conversation records unaffected.

• If, however, you rely on the relay service’s built-in session caching or implicit state storage, then switching endpoints will often cause the model to “forget” previous dialogue content.

How to achieve a seamless switch via ANTHROPIC_BASE_URL configuration?

You only need to change one environment variable to update the API request address:

export ANTHROPIC_BASE_URL="https://your-proxy.example.com"
export ANTHROPIC_API_KEY="your_token"

In production, inject these via container environment variables or Kubernetes Secrets — no repackaging required. Changing the address itself takes just ten seconds, but to get an experience identical to the official API, the following six checks are essential:

Why does switching relays cause Prompt Cache to fail and costs to double?

If you notice that “just changing the relay address doubles input token costs,” it’s usually because Prompt Cache hit rate has dropped to zero. Common causes fall into three categories:

Cause 1: Request body is rewritten (most common)

Cache/billing discounts typically require highly consistent input content. If the proxy makes any changes to the following fields, cache misses are highly likely:

• system prompt (even adding an audit log line)

• tools definitions (field order, whitespace, description changes)

• messages history (serialisation differences)

• model name (alias mapping / automatic substitution)

Cause 2: Cache scope is not reusable across providers/endpoints

Even if your requests are identical, different relays or providers do not necessarily share the same cache namespace — this is an architectural fact, not a bug.

Cause 3: Retries / timeouts / streaming buffering cause “double billing”

Cost increases are not always due to cache misses:

• Proxy timeout too short → client retries → the same request is billed twice

• SSE buffering / broken streams → business side treats as failure and retries → costs rise

• Rate limiting triggers automatic route switching without idempotency → request replay

How to achieve multi-model routing and session stickiness with a unified API gateway?

When a team uses more than just one model, the challenge shifts from “forwarding” to “preserving context and controlling costs while switching.”
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A qualified LLM unified gateway must at least deliver three things:

1. Session stickiness: The sameconversation_id / user_id / project_id is pinned to a fixed upstream within a time window, avoiding random drift.

2. Byte‑level pass‑through: No injection into system, no implicit model name remapping, no rewriting of tools—otherwise cache performance is inevitably compromised.

3. Cost observability and alerting: Provide usage metrics per model / route / tenant, and alert on abnormal fluctuations (e.g., tokens per request >15% change).

Just forwarding traffic doesn’t make a gateway; meeting the three requirements above is what qualifies it to support production switching.

Routescope core capabilities explained

Provides a unified entry point that is fully compatible with the Anthropic protocol, with intelligent multi‑upstream routing internally — no SDK changes required on the business side. Core advantages that directly address relay usage needs:

• Session stickiness: Bind upstream by conversation_id / user_id / project_id; common setting is "no drift within a 30‑minute window per session," which prevents prompt variation and style jumps at their source.

• Multi‑upstream + failover: Automatically switch to backup lines on timeout or rate limiting; the same session preferentially stays on the same line, so you don’t switch between three providers in a single conversation.

• Pass‑through fidelity: No injection into system, no implicit model name mapping—request bodies are sent out byte‑for‑byte as‑is. This is a prerequisite for Prompt Cache hits.

• Cost governance and observability: Provide usage reports across model / route / tenant dimensions. The most common team setup is hourly cost snapshots plus alerts when tokens per request fluctuate over 15%, so cache failures are detected within the hour — no need to wait until month‑end to see the bill.

• Policy‑based routing: Long‑context traffic goes to large‑window models, low‑value requests go to cheaper routes. Turn “don’t double the bill” into a rule, rather than relying on manual oversight.

Bottom line: The value of a gateway is to turn the switching actions scattered across environment variables, scripts, and operational know‑how into a configurable, observable, and rollback‑capable mechanism.

Summary

Changing the API relay for Claude Code is by no means just replacing a domain name. The core is to guarantee:

• Session context: either carry messages explicitly or ensure session stickiness.

• Prompt Cache: request body consistency (ensure system / tools / messages / model are not rewritten).

• Cost stability: avoid double billing from retries/replays, SSE buffering, and overly short timeouts.

Suggested process: start with a small‑scale grey‑level switch via ANTHROPIC_BASE_URL → run through the six acceptance checks → monitor conversation continuity, tool calls, and token costs → then roll out fully.

FAQ

I changed ANTHROPIC_BASE_URL but it doesn't take effect—why?

Most likely the environment variable isn't being read by the process—you exported it in the terminal, but the service was started from an old shell or via systemd. First confirm the variable is actually present in the process environment, then check whether the URL ends with an extra /v1 (some relays require it, others don't; an extra segment returns 404).

Can I use a free Claude Code relay long‑term?

You can get it working in the short term, but free routes generally do not guarantee unbuffered SSE, nor do they promise not to rewrite system—Prompt Cache hit rates often approach zero. What you save in subscription fees, you'll spend on token costs. For long‑term use, at least confirm that the provider is passing through requests unchanged.

How can I tell if a relay is secretly modifying my requests?

The quickest method is to normalise the request body to JSON, compute its hash, and compare before and after the switch. With a gateway, it’s even easier — entry points like Routescope that guarantee byte‑level pass‑through eliminate this risk upfront.