diff --git a/Cargo.lock b/Cargo.lock
index e6dc532b5..f097c88e9 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -144,7 +144,7 @@ version = "0.39.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "057ae90e7256ebf85f840b1638268df0142c9d19467d500b790631fd301acc27"
 dependencies = [
- "bit-set",
+ "bit-set 0.8.0",
  "regex",
  "thiserror 2.0.18",
  "tree-sitter",
@@ -215,15 +215,30 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "bit-set"
+version = "0.5.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0700ddab506f33b20a03b13996eccd309a48e5ff77d0d95926aa0210fb4e95f1"
+dependencies = [
+ "bit-vec 0.6.3",
+]
+
 [[package]]
 name = "bit-set"
 version = "0.8.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "08807e080ed7f9d5433fa9b275196cfc35414f66a0c79d864dc51a0d825231a3"
 dependencies = [
- "bit-vec",
+ "bit-vec 0.8.0",
 ]
 
+[[package]]
+name = "bit-vec"
+version = "0.6.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "349f9b6a179ed607305526ca489b34ad0a41aed5f7980fa90eb03160b69598fb"
+
 [[package]]
 name = "bit-vec"
 version = "0.8.0"
@@ -288,7 +303,7 @@ dependencies = [
  "cfg-if",
  "chrono",
  "clap",
- "fancy-regex",
+ "fancy-regex 0.16.2",
  "futures",
  "itertools",
  "nix 0.30.1",
@@ -315,7 +330,7 @@ dependencies = [
  "chrono",
  "clap",
  "command-fds",
- "fancy-regex",
+ "fancy-regex 0.16.2",
  "futures",
  "getrandom 0.3.4",
  "homedir",
@@ -794,13 +809,24 @@ version = "3.3.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "dea2df4cf52843e0452895c455a1a2cfbb842a1e7329671acf418fdc53ed4c59"
 
+[[package]]
+name = "fancy-regex"
+version = "0.13.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "531e46835a22af56d1e3b66f04844bed63158bc094a628bec1d321d9b4c44bf2"
+dependencies = [
+ "bit-set 0.5.3",
+ "regex-automata",
+ "regex-syntax",
+]
+
 [[package]]
 name = "fancy-regex"
 version = "0.16.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "998b056554fbe42e03ae0e152895cd1a7e1002aec800fdc6635d20270260c46f"
 dependencies = [
- "bit-set",
+ "bit-set 0.8.0",
  "regex-automata",
  "regex-syntax",
 ]
@@ -885,7 +911,7 @@ dependencies = [
  "fluent-syntax",
  "intl-memoizer",
  "intl_pluralrules",
- "rustc-hash",
+ "rustc-hash 2.1.2",
  "self_cell",
  "smallvec",
  "unic-langid",
@@ -1663,7 +1689,7 @@ dependencies = [
  "napi-build",
  "napi-sys",
  "nohash-hasher",
- "rustc-hash",
+ "rustc-hash 2.1.2",
  "tokio",
 ]
 
@@ -2172,6 +2198,7 @@ dependencies = [
  "similar",
  "smallvec",
  "syntect",
+ "tiktoken-rs",
  "tokio",
  "tokio-util",
  "toml",
@@ -2589,6 +2616,12 @@ dependencies = [
  "archery",
 ]
 
+[[package]]
+name = "rustc-hash"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "08d43f7aa6b08d49f382cde6a7982047c3426db949b1424bc4b7ec9ae12c6ce2"
+
 [[package]]
 name = "rustc-hash"
 version = "2.1.2"
@@ -2887,7 +2920,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "656b45c05d95a5704399aeef6bd0ddec7b2b3531b7c9e900abbf7c4d2190c925"
 dependencies = [
  "bincode",
- "fancy-regex",
+ "fancy-regex 0.16.2",
  "flate2",
  "fnv",
  "once_cell",
@@ -2990,6 +3023,21 @@ dependencies = [
  "zune-jpeg",
 ]
 
+[[package]]
+name = "tiktoken-rs"
+version = "0.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "25563eeba904d770acf527e8b370fe9a5547bacd20ff84a0b6c3bc41288e5625"
+dependencies = [
+ "anyhow",
+ "base64",
+ "bstr",
+ "fancy-regex 0.13.0",
+ "lazy_static",
+ "regex",
+ "rustc-hash 1.1.0",
+]
+
 [[package]]
 name = "tiny-keccak"
 version = "2.0.2"
@@ -3722,7 +3770,7 @@ version = "0.5.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cb30dbbd9036155e74adad6812e9898d03ec374946234fbcebd5dfc7b9187b90"
 dependencies = [
- "rustc-hash",
+ "rustc-hash 2.1.2",
 ]
 
 [[package]]
diff --git a/crates/pi-natives/Cargo.toml b/crates/pi-natives/Cargo.toml
index 6156ac043..216f0ec45 100644
--- a/crates/pi-natives/Cargo.toml
+++ b/crates/pi-natives/Cargo.toml
@@ -119,6 +119,7 @@ smallvec = { version = "1.15.1", features = [
 memmap2 = "0.9"
 xxhash-rust = { version = "0.8", features = ["xxh64"] }
 regex = "1"
+tiktoken-rs = "0.7"
 similar = "3.0.0"
 serde = { version = "1.0", features = ["derive"] }
 serde_json = { version = "1.0", features = ["preserve_order"] }
diff --git a/crates/pi-natives/src/lib.rs b/crates/pi-natives/src/lib.rs
index d89dca487..53589d38a 100644
--- a/crates/pi-natives/src/lib.rs
+++ b/crates/pi-natives/src/lib.rs
@@ -48,4 +48,5 @@ pub mod pty;
 pub mod shell;
 pub mod task;
 pub mod text;
+pub mod tokens;
 pub(crate) mod utils;
diff --git a/crates/pi-natives/src/tokens.rs b/crates/pi-natives/src/tokens.rs
new file mode 100644
index 000000000..03270451b
--- /dev/null
+++ b/crates/pi-natives/src/tokens.rs
@@ -0,0 +1,65 @@
+//! Token counting via tiktoken-rs.
+//!
+//! Two encodings are exposed:
+//!
+//!   - `O200kBase` — GPT-4o / o1 / GPT-5 (the modern OpenAI default).
+//!   - `Cl100kBase` — GPT-3.5 / GPT-4 / older models.
+//!
+//! `o200k_base` is the default. Anthropic doesn't publish their tokenizer, so
+//! either of these is an approximation for Claude (within ~5–10% across
+//! English/code text). `o200k_base` is closer to current frontier models'
+//! actual segmentation and is the right default for budget estimates.
+//!
+//! Both BPE tables are embedded in the binary; encoders are built once on
+//! first use and reused thereafter.
+
+use std::sync::LazyLock;
+
+use napi::bindgen_prelude::Either;
+use napi_derive::napi;
+use rayon::prelude::*;
+use tiktoken_rs::{CoreBPE, cl100k_base, o200k_base};
+
+/// Tokenizer encoding to use.
+#[napi(string_enum)]
+pub enum Encoding {
+	/// GPT-4o / o1 / GPT-5 (default).
+	O200kBase,
+	/// GPT-3.5 / GPT-4 / older.
+	Cl100kBase,
+}
+
+static O200K: LazyLock<CoreBPE> =
+	LazyLock::new(|| o200k_base().expect("failed to initialize o200k_base BPE tables"));
+
+static CL100K: LazyLock<CoreBPE> =
+	LazyLock::new(|| cl100k_base().expect("failed to initialize cl100k_base BPE tables"));
+
+fn encoder(encoding: Option<Encoding>) -> &'static CoreBPE {
+	match encoding.unwrap_or(Encoding::O200kBase) {
+		Encoding::O200kBase => &O200K,
+		Encoding::Cl100kBase => &CL100K,
+	}
+}
+
+/// Count tokens in `input`.
+///
+/// `input` may be a single string or an array of strings; an array returns
+/// the sum across all elements (encoded in parallel via rayon). Always
+/// returns a single token total — use this for any aggregate budget question
+/// without paying a per-element napi crossing.
+///
+/// Uses ordinary encoding (no special-token handling), which is the right
+/// choice for measuring user/model content rather than wire-protocol tokens.
+/// Defaults to `o200k_base`; pass `Cl100kBase` for older OpenAI models.
+#[napi]
+pub fn count_tokens(input: Either<String, Vec<String>>, encoding: Option<Encoding>) -> u32 {
+	let bpe = encoder(encoding);
+	match input {
+		Either::A(text) => bpe.encode_ordinary(&text).len() as u32,
+		Either::B(texts) => texts
+			.par_iter()
+			.map(|s| bpe.encode_ordinary(s).len() as u32)
+			.sum(),
+	}
+}
diff --git a/packages/natives/native/index.d.ts b/packages/natives/native/index.d.ts
index 3dca5c6c4..599cd2e8a 100644
--- a/packages/natives/native/index.d.ts
+++ b/packages/natives/native/index.d.ts
@@ -310,6 +310,20 @@ export interface ContextLine {
  */
 export declare function copyToClipboard(text: string): void
 
+/**
+ * Count tokens in `input`.
+ *
+ * `input` may be a single string or an array of strings; an array returns
+ * the sum across all elements (encoded in parallel via rayon). Always
+ * returns a single token total — use this for any aggregate budget question
+ * without paying a per-element napi crossing.
+ *
+ * Uses ordinary encoding (no special-token handling), which is the right
+ * choice for measuring user/model content rather than wire-protocol tokens.
+ * Defaults to `o200k_base`; pass `Cl100kBase` for older OpenAI models.
+ */
+export declare function countTokens(input: string | Array<string>, encoding?: Encoding | undefined | null): number
+
 /**
  * Detect macOS system appearance via CoreFoundation.
  * Returns `"dark"` or `"light"` on macOS, `null` on other platforms.
@@ -337,6 +351,14 @@ export declare enum Ellipsis {
  */
 export declare function encodeSixel(bytes: Uint8Array, targetWidthPx: number, targetHeightPx: number): string
 
+/** Tokenizer encoding to use. */
+export declare enum Encoding {
+  /** GPT-4o / o1 / GPT-5 (default). */
+  O200kBase = 'O200kBase',
+  /** GPT-3.5 / GPT-4 / older. */
+  Cl100kBase = 'Cl100kBase'
+}
+
 /**
  * Execute a brush shell command.
  *
diff --git a/packages/natives/native/index.js b/packages/natives/native/index.js
index ef7b00235..3703ad5f6 100644
--- a/packages/natives/native/index.js
+++ b/packages/natives/native/index.js
@@ -238,6 +238,10 @@ module.exports.Ellipsis = {
   Ascii: 1,
   Omit: 2,
 };
+module.exports.Encoding = {
+  O200kBase: 'O200kBase',
+  Cl100kBase: 'Cl100kBase',
+};
 module.exports.FileType = {
   File: 1,
   Dir: 2,