diff --git a/src/transition.c b/src/transition.c
index 6521a612c8..56c11ac4d2 100644
--- a/src/transition.c
+++ b/src/transition.c
@@ -10,132 +10,6 @@
 #include "transition.h"
 #include "utils.h"
 
-double animatable_get_progress(const struct animatable *a) {
-	if (a->duration > 0) {
-		return a->elapsed / a->duration;
-	}
-	return 1;
-}
-
-/// Get the current value of an `animatable`.
-double animatable_get(const struct animatable *a) {
-	if (a->duration > 0) {
-		assert(a->elapsed < a->duration);
-		double t = a->curve->sample(a->curve, animatable_get_progress(a));
-		return (1 - t) * a->start + t * a->target;
-	}
-	return a->target;
-}
-
-/// Advance the animation by a given number of steps.
-void animatable_advance(struct animatable *a, double elapsed) {
-	if (a->duration == 0 || elapsed <= 0) {
-		return;
-	}
-
-	assert(a->elapsed < a->duration);
-	if (elapsed >= a->duration - a->elapsed) {
-		a->elapsed = a->duration;
-	} else {
-		a->elapsed += elapsed;
-	}
-
-	if (a->elapsed == a->duration) {
-		a->start = a->target;
-		a->duration = 0;
-		a->elapsed = 0;
-		a->curve->free(a->curve);
-		a->curve = NULL;
-		if (a->callback) {
-			a->callback(TRANSITION_COMPLETED, a->callback_data);
-			a->callback = NULL;
-			a->callback_data = NULL;
-		}
-	}
-}
-
-/// Returns whether an `animatable` is currently animating.
-bool animatable_is_animating(const struct animatable *a) {
-	assert(a->duration == 0 || a->elapsed < a->duration);
-	return a->duration != 0;
-}
-
-/// Cancel the current animation of an `animatable`. This stops the animation and
-/// the `animatable` will retain its current value.
-///
-/// Returns true if the `animatable` was animated before this function is called.
-bool animatable_interrupt(struct animatable *a) {
-	if (a->duration == 0) {
-		return false;
-	}
-
-	a->start = animatable_get(a);
-	a->target = a->start;
-	a->duration = 0;
-	a->elapsed = 0;
-	a->curve->free(a->curve);
-	a->curve = NULL;
-	if (a->callback) {
-		a->callback(TRANSITION_INTERRUPTED, a->callback_data);
-		a->callback = NULL;
-		a->callback_data = NULL;
-	}
-	return true;
-}
-
-/// Cancel the current animation of an `animatable` and set its value to its target.
-///
-/// Returns true if the `animatable` was animated before this function is called.
-bool animatable_skip(struct animatable *a) {
-	if (a->duration == 0) {
-		return false;
-	}
-
-	a->start = a->target;
-	a->duration = 0;
-	a->elapsed = 0;
-	a->curve->free(a->curve);
-	a->curve = NULL;
-	if (a->callback) {
-		a->callback(TRANSITION_SKIPPED, a->callback_data);
-		a->callback = NULL;
-		a->callback_data = NULL;
-	}
-	return true;
-}
-
-/// Change the target value of an `animatable`.
-/// If the `animatable` is already animating, the animation will be canceled first.
-bool animatable_set_target(struct animatable *a, double target, double duration,
-                           const struct curve *curve, transition_callback_fn cb, void *data) {
-	animatable_interrupt(a);
-	if (duration == 0 || a->start == target) {
-		a->start = target;
-		a->target = target;
-		curve->free(curve);
-		return false;
-	}
-
-	a->target = target;
-	a->duration = duration;
-	a->elapsed = 0;
-	a->callback = cb;
-	a->callback_data = data;
-	a->curve = curve;
-	return true;
-}
-
-/// Create a new animatable.
-struct animatable animatable_new(double value) {
-	struct animatable ret = {
-	    .start = value,
-	    .target = value,
-	    .duration = 0,
-	    .elapsed = 0,
-	};
-	return ret;
-}
-
 static double curve_sample_linear(const struct curve *this attr_unused, double progress) {
 	return progress;
 }
diff --git a/src/transition.h b/src/transition.h
index b5131f4b7f..d6bcab299f 100644
--- a/src/transition.h
+++ b/src/transition.h
@@ -5,31 +5,7 @@
 #include <stdbool.h>
 #include "compiler.h"
 
-struct animatable;
-enum transition_event;
-
-/// Callback when the transition state changes. Callback might be called by:
-///   - `animatable_set_target` generates TRANSITION_COMPLETED when the specified duration
-///     is 0. also generates TRANSITION_CANCELLED if the animatable was already animating.
-///   - `animatable_cancel` generates TRANSITION_CANCELED
-///   - `animatable_early_stop` generates TRANSITION_STOPPED_EARLY
-///   - `animatable_step` generates TRANSITION_COMPLETED when the animation is completed.
-/// Callback is guaranteed to be called exactly once for each `animatable_set_target`
-/// call, unless an animatable is freed before the transition is completed.
-typedef void (*transition_callback_fn)(enum transition_event event, void *data);
-
-enum transition_event {
-	TRANSITION_COMPLETED,
-	TRANSITION_INTERRUPTED,
-	TRANSITION_SKIPPED,
-};
-
-/// The base type for step_state.
-struct step_state_base {
-	/// The current value of the `animatable`.
-	/// If the `animatable` is not animated, this equals to `animatable->target`.
-	double current;
-};
+// ========================== Interpolators ==========================
 
 struct curve {
 	/// The interpolator function for an animatable. This function should calculate
@@ -40,68 +16,6 @@ struct curve {
 	void (*free)(const struct curve *this);
 };
 
-/// An animatable value
-struct animatable {
-	/// The starting value.
-	/// When this `animatable` is not animated, this is the current value.
-	double start;
-	/// The target value.
-	/// If the `animatable` is not animated, this equals to `start`.
-	double target;
-	/// The animation duration in unspecified units.
-	/// If the `animatable` is not animated, this is 0.
-	double duration;
-	/// The current progress of the animation in the same units as `duration`.
-	/// If the `animatable` is not animated, this is 0.
-	double elapsed;
-
-	transition_callback_fn callback;
-	void *callback_data;
-
-	/// The function for calculating the current value. If
-	/// `step_state` is not NULL, the `step` function is used;
-	/// otherwise, the `interpolator` function is used.
-	/// The interpolator function.
-	const struct curve *curve;
-};
-
-// =============================== API ===============================
-
-/// Get the current value of an `animatable`.
-double animatable_get(const struct animatable *a);
-/// Get the animation progress as a percentage of the total duration.
-double animatable_get_progress(const struct animatable *a);
-/// Advance the animation by a given amount. `elapsed` cannot be negative.
-void animatable_advance(struct animatable *a, double elapsed);
-/// Returns whether an `animatable` is currently animating.
-bool animatable_is_animating(const struct animatable *a);
-/// Interrupt the current animation of an `animatable`. This stops the animation and
-/// the `animatable` will retain its current value.
-///
-/// Returns true if the `animatable` was animated before this function is called.
-bool animatable_interrupt(struct animatable *a);
-/// Skip the current animation of an `animatable` and set its value to its target.
-///
-/// Returns true if the `animatable` was animated before this function is called.
-bool animatable_skip(struct animatable *a);
-/// Change the target value of an `animatable`. Specify a duration, an interpolator
-/// function, and a callback function.
-///
-/// If the `animatable` is already animating, the animation will be canceled first.
-///
-/// Note, In some cases this function does not start the animation, for example, if the
-/// target value is the same as the current value of the animatable, or if the duration is
-/// 0. If the animation is not started, the callback function will not be called. The
-/// animatable's current animation, if it has one, will be canceled regardless.
-///
-/// Returns if the animatable is now animated.
-bool animatable_set_target(struct animatable *a, double target, double duration,
-                           const struct curve *curve, transition_callback_fn cb, void *data);
-/// Create a new animatable.
-struct animatable animatable_new(double value);
-
-// ========================== Interpolators ==========================
-
 const struct curve *curve_new_linear(void);
 const struct curve *curve_new_cubic_bezier(double x1, double y1, double x2, double y2);
 const struct curve *curve_new_step(int steps, bool jump_start, bool jump_end);