/**
 * anthropic-beta header filtering for Max vs API profiles.
 *
 * Some betas (e.g. `extended-cache-ttl-*`) trigger Extra-Usage billing on
 * Claude Max subscriptions. The default `allow-safe` policy strips only those
 * for claude-max profiles while forwarding everything else so that prompt
 * caching, 1M context, fine-grained tool streaming, and interleaved thinking
 * continue to work as the SDK expects.
 *
 * Unconditional stripping (the previous behaviour) caused cache misses on
 * every turn, which tripled TTFB and inflated token consumption roughly 3x on
 * long conversations. See issue #278 for the original context.
 *
 * An operator can override the policy at runtime via the `MERIDIAN_BETA_POLICY`
 * env var to force `strip-all` (safest — old behaviour) or `allow-all`
 * (most permissive — matches api-profile behaviour) without a rebuild.
 *
 * This module is pure — no I/O, no imports from server.ts or session/.
 */
import type { ProfileType } from "./profiles";
/**
 * Beta prefixes that are known to trigger Extra-Usage billing on Max accounts.
 *
 * A beta is considered billable if its name starts with any of these strings.
 * Keep this list conservative — prefer allowing unknown betas through over
 * silently stripping something the SDK needs for normal operation.
 */
export declare const BILLABLE_BETA_PREFIXES_ON_MAX: readonly string[];
/**
 * Runtime policy for `anthropic-beta` header handling on claude-max profiles.
 *
 * - `allow-safe` (default): forward all betas except those matching
 *   {@link BILLABLE_BETA_PREFIXES_ON_MAX}. Restores prompt caching + 1M
 *   context while keeping the original billing-safety intent.
 * - `strip-all`: the pre-fix (1.28.0 – 1.29.x) behaviour. Drops every beta
 *   for claude-max profiles. Use this as a kill switch if the allow-safe
 *   policy ever causes quota surprises.
 * - `allow-all`: forward every beta unconditionally, same as api profiles.
 *   Use only if you've verified your Max tier treats all betas as free.
 */
export type BetaPolicy = "allow-safe" | "strip-all" | "allow-all";
export declare const DEFAULT_BETA_POLICY: BetaPolicy;
export interface BetaFilterResult {
    /** Betas to forward upstream. `undefined` means no header should be sent. */
    forwarded: string[] | undefined;
    /** Betas that were removed. Empty for api-type profiles. */
    stripped: string[];
}
/**
 * Read the beta policy from the `MERIDIAN_BETA_POLICY` env var.
 *
 * Falls back to {@link DEFAULT_BETA_POLICY} for missing or invalid values.
 * Invalid values are silently ignored rather than crashing the proxy.
 */
export declare function getBetaPolicyFromEnv(): BetaPolicy;
/**
 * Filter an `anthropic-beta` header value for the given profile type.
 *
 * - For `api` profiles, all betas pass through unchanged regardless of policy.
 * - For `claude-max` profiles, behaviour depends on `policy`:
 *   - `allow-safe` (default): strip only billable betas
 *     (see {@link BILLABLE_BETA_PREFIXES_ON_MAX}).
 *   - `strip-all`: strip every beta.
 *   - `allow-all`: forward every beta unchanged.
 * - Whitespace and empty entries are trimmed.
 * - Returns `forwarded: undefined` when the result would be an empty list so
 *   callers can omit the header entirely.
 */
export declare function filterBetasForProfile(rawBetaHeader: string | undefined, profileType: ProfileType, policy?: BetaPolicy): BetaFilterResult;
//# sourceMappingURL=betas.d.ts.map