diff --git a/rfcs/v4-issue-formats/old_formats.ts b/rfcs/v4-issue-formats/old_formats.ts
new file mode 100644
index 000000000..46cf69f14
--- /dev/null
+++ b/rfcs/v4-issue-formats/old_formats.ts
@@ -0,0 +1,152 @@
+type ZodParsedType = string;
+type Primitive = string | number | boolean | bigint | symbol | undefined | null;
+class ZodError {}
+
+export enum ZodIssueCode {
+  invalid_type = "invalid_type",
+  invalid_literal = "invalid_literal",
+  custom = "custom",
+  invalid_union = "invalid_union",
+  invalid_union_discriminator = "invalid_union_discriminator",
+  invalid_enum_value = "invalid_enum_value",
+  unrecognized_keys = "unrecognized_keys",
+  invalid_arguments = "invalid_arguments",
+  invalid_return_type = "invalid_return_type",
+  invalid_date = "invalid_date",
+  invalid_string = "invalid_string",
+  too_small = "too_small",
+  too_big = "too_big",
+  invalid_intersection_types = "invalid_intersection_types",
+  not_multiple_of = "not_multiple_of",
+  not_finite = "not_finite",
+}
+
+export type ZodIssueBase = {
+  path: (string | number)[];
+  message?: string;
+  fatal?: boolean;
+};
+
+export interface ZodInvalidTypeIssue extends ZodIssueBase {
+  code: typeof ZodIssueCode.invalid_type;
+  expected: ZodParsedType;
+  received: ZodParsedType;
+}
+
+export interface ZodInvalidLiteralIssue extends ZodIssueBase {
+  code: typeof ZodIssueCode.invalid_literal;
+  expected: unknown;
+  received: unknown;
+}
+
+export interface ZodUnrecognizedKeysIssue extends ZodIssueBase {
+  code: typeof ZodIssueCode.unrecognized_keys;
+  keys: string[];
+}
+
+export interface ZodInvalidUnionIssue extends ZodIssueBase {
+  code: typeof ZodIssueCode.invalid_union;
+  unionErrors: ZodError[];
+}
+
+export interface ZodInvalidUnionDiscriminatorIssue extends ZodIssueBase {
+  code: typeof ZodIssueCode.invalid_union_discriminator;
+  options: Primitive[];
+}
+
+export interface ZodInvalidEnumValueIssue extends ZodIssueBase {
+  received: string | number;
+  code: typeof ZodIssueCode.invalid_enum_value;
+  options: (string | number)[];
+}
+
+export interface ZodInvalidArgumentsIssue extends ZodIssueBase {
+  code: typeof ZodIssueCode.invalid_arguments;
+  argumentsError: ZodError;
+}
+
+export interface ZodInvalidReturnTypeIssue extends ZodIssueBase {
+  code: typeof ZodIssueCode.invalid_return_type;
+  returnTypeError: ZodError;
+}
+
+export interface ZodInvalidDateIssue extends ZodIssueBase {
+  code: typeof ZodIssueCode.invalid_date;
+}
+
+export type StringValidation =
+  | "email"
+  | "url"
+  | "emoji"
+  | "uuid"
+  | "nanoid"
+  | "regex"
+  | "cuid"
+  | "cuid2"
+  | "ulid"
+  | "datetime"
+  | "date"
+  | "time"
+  | "duration"
+  | "ip"
+  | "base64"
+  | { includes: string; position?: number }
+  | { startsWith: string }
+  | { endsWith: string };
+
+export interface ZodInvalidStringIssue extends ZodIssueBase {
+  code: typeof ZodIssueCode.invalid_string;
+  validation: StringValidation;
+}
+
+export interface ZodTooSmallIssue extends ZodIssueBase {
+  code: typeof ZodIssueCode.too_small;
+  minimum: number | bigint;
+  inclusive: boolean;
+  exact?: boolean;
+  type: "array" | "string" | "number" | "set" | "date" | "bigint";
+}
+
+export interface ZodTooBigIssue extends ZodIssueBase {
+  code: typeof ZodIssueCode.too_big;
+  maximum: number | bigint;
+  inclusive: boolean;
+  exact?: boolean;
+  type: "array" | "string" | "number" | "set" | "date" | "bigint";
+}
+
+export interface ZodInvalidIntersectionTypesIssue extends ZodIssueBase {
+  code: typeof ZodIssueCode.invalid_intersection_types;
+}
+
+export interface ZodNotMultipleOfIssue extends ZodIssueBase {
+  code: typeof ZodIssueCode.not_multiple_of;
+  multipleOf: number | bigint;
+}
+
+export interface ZodNotFiniteIssue extends ZodIssueBase {
+  code: typeof ZodIssueCode.not_finite;
+}
+
+export interface ZodCustomIssue extends ZodIssueBase {
+  code: typeof ZodIssueCode.custom;
+  params?: { [k: string]: any };
+}
+
+export type ZodIssue =
+  | ZodInvalidTypeIssue
+  | ZodInvalidLiteralIssue
+  | ZodUnrecognizedKeysIssue
+  | ZodInvalidUnionIssue
+  | ZodInvalidUnionDiscriminatorIssue
+  | ZodInvalidEnumValueIssue
+  | ZodInvalidArgumentsIssue
+  | ZodInvalidReturnTypeIssue
+  | ZodInvalidDateIssue
+  | ZodInvalidStringIssue
+  | ZodTooSmallIssue
+  | ZodTooBigIssue
+  | ZodInvalidIntersectionTypesIssue
+  | ZodNotMultipleOfIssue
+  | ZodNotFiniteIssue
+  | ZodCustomIssue;